ute doors wont fit the coupe... only coupe doors do.
as for parts interchangeability... starter motor fit and works fine, as does flywheel and depending on which gx head you have the extractors may fit... just with the assistance of an angle grinder to trim the excess off so the inlet manifold will go on as well.

best radiators for a15... gemini or n14 pulsar... im looking at a sigma one now though and it may just fit uder the bonnet ... its pretty tall. Also have a ae86 raditor in the shed but looks very thin ...