You couldnt make a GTS a GTR, bodys are totally different, and if you miss it, your stupid.

Yould could put a GTST engine in a base GTS but so what.

GTS 2.5 RWD
GTR 2.6 4WD
Different engines, different blocks n heads (well they share no common parts), both capable of huge 700+ power, just GTRs need a lot less things changing for the power.

Main advantage of GTRs is the transmission