As far as I have been able to find out, the roof is the same between both 4 and 2 door cars. So the only things I can tell that are different would be the length of the door (it would be longer by about 4-5 inches), the side glass (both front and back), and the pillar which the door closes against will need to be moved further back. You may be able to unstich the pillar from the frame and reweld it in its new location. You would also need to find a two door shell to use the rear quarter panels from with the correct opening for the rear window.

I honestly belive it would be easier to locate a two door and put all your gear into that one.

How is the SR20 conversion coming along? it's been a while since i have heard from you, all good I hope.

Cheers Mitchell