the engines are all the same in the 32gtst's...the differences are in the interior. 89 models have blue guages, diff seating trim and a diff type of plastic around the radio console, which looks pretty crappy.
the older models also have RB20 embossed in the cam cover.
also try pik up a Type M gtst...the type M came with 4 piston front callipers and 2 piston rear, and also type M skirts and rear pods.
try and get the newest model with as lil' k's as possible, and very lil' mods. nuthin wrong with pikin up a lightly modified one...just be cautious of ones running high boost on the stock turbo etc...
and remember parts can be tricky and expensive to get for a skyline...so if u find one that needs lil' bits replaced...dont just think, 'np, ill just get that part from the wreckers'. hehe
good luck