No need to be complicate on this one, the easy way is the best way. Just pull the adapter off, put the filter back on, and the engine side is done. www.siegecraft.us/mocal.htm
for some photos of what things look like on a '94. I would then put some plugs on the radiator side fittings after removing the hoses, just to keep the now unused cooler from getting contaminated over time.
Definitely do NOT take off the lines and plug them on the engine adapter, with the adapter on it is the only
flowpath for the oil, and it will destroy the engine bearings in just a minute or two of running.
Oh, and that part you linked to, I have no idea what that thing is. Looks nothing like the oil pump base on my truck, not even close. Definitely not a part off of a 3.9 oil pump assembly. Maybe comes off of a 4.0? The oil system on the 4.0 is totally different than on a 3.9.