sorry to bring this back up, it's not that old thou. the DET head isn't worth modding to fit the ET block. i don't remember all the details but far to much work is involved to be plactical. their was something to do with the combustion chamber and stuff about the dizzy. club-s12.org has a thread some were that talks about this. or it did, don't know if it survived the crash we had. we have a member in the club that is right around 300hp over in Boise. he's working on going higher but keeps blowing head gaskets right now. he has built alot of custom performance parts for the 1.8t s12's.
the reason that the s12 is not popular, so say we s12 drivers, is that the AE86 is the main car in Initial D. with that shows growing popularity, more and more people are turning to the 86. if the s12 was put into something and was raised up for it's capability, it would be more comonly used.
as far as the rear end is concerned, the R200 and R180 in the CA cars have a 4.11 gear ratio. the R200 came in the turbo car and the R180 came in the n/a CA20E car. the R200 in the VG powered car has i think a 3.9 gear, something right around their. the whole rear suspention is the same as the z31.