I worked up a step-by-step list for this conversion. I plan on documenting it here just because it is fun and someone might benefit. I usually benefit the most from my mistakes along the way, so perhaps this will help others.
Here is my checklist. I used Nick's list in the adapter thread and built on it. I'll reference this list by step number along the way and I'd love any suggestions or changes you see if you take the time to read through all of it. This is for my conversion of a 1988 D90 with a turbo diesel (19J) and LT77 to an L99/6L80 from a 20k mile 2012 Camaro.
Some install tips and order:
1. Disconnect the negative battery cable, remove the hood and front grill. Drain and remove the radiator, surge tank and all brackets. Capture all fasteners and small parts in ziplock bags labeled with a sharpie.
2. Disconnect the prop. shafts, e-brake cable, speedometer cable, throttle cable and all electrical connections, carefully labeling each wire with masking tape. Disconnect and drain the clutch master cylinder at the slave. Once drained, seal the slave. Clutch fluid will remove paint almost immediately!
3. Drain and disconnect the power steering reservoir and pump, sealing all pump connections.
4. Disconnect the fuel supply and return lines at the lift pump and remove the firewall mounted filter, lines and fuel tank.
5. Connect an engine hoist with an engine leveler to the engine and ensure it is properly connected to four SECURE points, two on the front and two on the rear of the engine. Adjust the leveler so that the engine hoist lifting hook is as close to the rear of the engine as possible and use the hoist to take all the slack out of the leveler lifting chains. Remove the crossmember and unbolt the four mounts holding the engine and transmission to the chassis. A floor jack may be helpful in lifting the transmission enough to clear the mounts until you can move the whole assembly forward with the hoist. Remove the engine and transmission as a unit.
6. Remove the steering box and rebuild or replace as required, reinstalling a leak free unit (you know the original has leaked for years!) after step #7.
7. Inspect the engine bay, removing any items not required (old mounts, brackets, diesel components, clutch master and pedal, etc.). Weld in the new frame motor mounts, clean the engine bay, install the clutch block off plate and prime/paint as required. Now is the time to make it spiffy!
8. Remove the exhaust manifolds from the LS3. You will end up slamming them into the steering linkage on the way in. It also gives you access to the engine mounts. The stock exhaust manifolds are discarded.
9. Remove the intake manifold. It needs to be rotated 180 degrees anyway. Too much risk of getting damaged. NOTE: Not if LS3 donor from car.
10. Remove any shifter linkage (transfer case and transmission) These can be installed from the tunnel opening.
11. Install the harness on the engine and connect the transmission connector prior to bolting up the LT230. The transfer case traps the transmission electrical connector.
12. Leave the engine mounts (Energy Suspension and aluminum plate) loose to allow alignment.
13. Leave the power steering pump off until engine has been installed. Too much risk smashing it on the steering box.
14. Install the adapter onto the transmission first. Then the LT230 onto the adapter. Don't forget the two alignment dowels between the adapter and LT230. Also, the two 40mm bolts need sealant as they are open to gear oil. The tail housing is dry, so no gaskets required there. Good time to install a new input shaft seal in the LT230.
15. If possible, drop in the engine/transmission/LT230 in one shot. Else, engine/transmission in one shot.
16. Level the engine and bolt the engine, TC, and adapter frame mounts to torque spec. Bolt up the prop. shafts and check for clearance (in a lowered vehicle, the best approach is to disconnect the front prop. shaft at the differential and move it up and down through the normal arc travelled during suspension movement to ensure clearance). Adjust or trim any obstacles such as the transmission bell housing and oil pan. Install the motor mount heat shields.
17. Reinstall or fabricate as required a new crossmember. If fabricating, adjust as required to optimize exhaust routing (step 19).
18. Install the modified fuel tank with in tank pump and new sender. Install filter/regulator on firewall, fabricate twist lock hoses and install supply, return and fuel rail feed. Secure all fuel lines safely, shielding from heat and any potential debris from the wheels.
19. Install headers and fabricate the exhaust system, carefully removing or isolating any electronics (ecu, etc) before welding. Tack on the car and remove each section for final welding, reinstalling each section after final welding to ensure proper fit.
20. Connect the Speartech modified harness connections, install fuses and relay, and connect to vehicle electrical system as required.
21. Configure accessory brackets, alternator, PS pump and A/C compressor as required to clear chassis, install and tension belt. Connect lines to power steering pump, reservoir, and steering box.
22. Install radiator, fan(s) and surge tank, fabricate and install all hoses to radiator, surge tank and heater ensuring all fittings and clamps are tight. Install the intake hose and filter, refitting the MAF sensor.
23. Install transmission cooler and run lines to transmission, securing them and shielding from any hazards.
24. Install A/C condenser and connect all A/C lines.
25. Install shifter, TC linkage and new gauges.
26. Double check everything!
27. Fill all fluids, bleed cooling system, reconnect negative cable, look for smoke (hey, it still has some Lucas components), and start the engine. NOTE: my wife now requires all first starts to happen outside the garage. Ever since the engine in the Cobra shot a fireball out of the carburetor due to the distributor being installed 180 out. Oops. For the record, it was a small fireball.
28. Take a short test drive before reinstalling the tunnel, hood, and other body parts removed for the conversion. Check for leaks, rubbing, and all other paranoid concerns created by a conversion of this magnitude.
29. Drink.
30. Well, that's all there is to it. A weekends worth of work...okay, so probably 100 hours if you are a reasonable shade tree, have the right parts and tools when you need them and don't get interrupted too many times or suffer from "whileIwasinthere" syndrome.