Thirdgen.org has several threads on this subject. Yes there are aftermarket K-members from BMR & Spohn for this, but on TGO they also document the mods you can make to a stock K-member to get it to work.
LS3's aren't cheap though. The cheapest all-in-one package out there is the E-Rod package and its $8400 for the engine, headers, harness & ECU. It'll be another $600 for the K-member and thats assuming you can salvage the accessories and what not from an LS1 4th gen. Assuming you can't and that the E-Rod supplied headers don't fit, its almost $2k for LSx swap headers for a third gen and a GMPP LS accessory drive kit.
There are alot of costs to look at before doing this kind of swap.
Project: 89 RS => AX/RR
Last edited by 89RS; 08-01-2010 at 06:31 PM.