Pretty much the same drivechain.... Even if it varies, i've spoken to fellow GTS4 owners who have put RB26's in them.
Diff is smaller (obviously)
The Box is tough as nail's and unless your going for enormous power it shouldnt ever give way
If your looking for coilovers for it, You need a set to suit an R33 GTS-T
You can easily do a 5 stud conversion and fit 18x9.5's on it without the tyres poking out the sides
Extractors are a great mod for them, KOBE which are sourced from NZ or just scour your local jap wreckers and you might be lucky.
Body kits are a total custom job, Only the front bar is availible "off the shelf"
The GTR is quicker, lighter ect, But with a bit of stupidity like me, you can embark on creating a 4 door monster
Buy it, Buy it!