After a bit more thought I'm pretty keen on keeping it in the BMW family and putting an M3 engine in, a friend of mine who has an M3 and knows alot about bmw says that it mechanically it should be an easy swap as the gearbox should match up without any dramas and i'd just need different engine mounts.. electrics and that stuff might be tricky, I dont know much (or anything really) about that.
I've also been looking at Z4's and considering the price of those it could be worth just getting an 03-05 (E85) Z4 and putting an S54(E46 M3) or S50B30(E36) engine in.
Apparantly the 3.0 or european 3.2 from E36 M3 is alot easier as it uses a single VANOS (BMW's version of vtec/mivec) for the intake valves where the S54 from the E46 M3 uses a double vanos for intake and exhaust valves which is more electrics and tricky bits
However the S54 engine is used in the Z4 M coupe/roadster such as
this one in WA for 65k, so it might not be too hard?
Either way, I've still gotta save up/pay off my skyline (3k to go) first before looking at getting one
