the sr20dets share alot between them.

i,e the same engine mounts will fit an s13/s14/s15

You can fit an s15/s14 gearbox to an s13 and vise-versa

The difference btw a s13 sr20det engine and s14/s15 is the vvti. The engine has a slightly different shape at the front but that shouldn't make a difference in a 1200 mate.hard to explain but wouldn't matter in a 1200 ute or in a silvia.

they are so many s13 running s14/s15 engines.esp conversions from non turbo to turbo.

Is this for a road going car or strictly race car?
check with the engineers of ur state on how to proceed ifs its a road going vehicle.