LS3's are in no way shape or form cheap.. Good luck with this but if it was gonna be expensive I personally would just make a fun car out of it..
And since you are looking into building a 3rd gen.. This might give you a few ideas or insight on a few things...
1987 Iroc, COMPLETE rebuild, 650+ rwhp, new paint, wheels, etc.(The blue one) - HorsepowerJunkies.com Forums