Matthew, it's not too hard to rotate the compressor housing and just drill and tap to put the wastegate actuator back where it needs to be. That way, even if you are using the disco hot side housing you can still get the compressor to point the right way to keep your engine bay stock looking. I'm pretty sure that the four bolt turbo-to-manifold flange of the Disco turbo will indeed bolt up to the defender manifold. I'm not sure where that puts the oil feed and drain openings, but the cartridge will rotate to get them back vertical. If it works that is a pretty good idea as it will make it much easier to fab a custom downpipe that uses the 3-bolt flange instead of the funk one that's on the defender turbos.
1960 SII 109"- "Red Square"
1984 90 Tdi- "Yamelo"
1988 RRC- "Chewbacca"
1987 RRC- "Chewy 2"
2008 RRS SC- "The Supersofa"
1959 SII 88"- "The Little Green Beastie" last seen in NY
1972 SIII 88"- "GreenHELL" now in NC
1988 90 "Eric the Half a Bee" half a truck, sold for parts
1991 RRC- never got a name- long since recycled