I would have thought you would be making your plans from the ground up, with the bigger considerations being handling (wheels/tyres/suspention) of the extra power on the move, and then the braking as I would have thought you were having to cope with at least 50% + extra power (dunno what the Monaro output is, sorry)
Am looking forward the the pictures when you start building.
Just thinking, Have a chat with B+H Autokraft in Doncaster they do a lot of yank V8 coversions. Run the idea past them (they may be cheaper than you thinkk for the LS engine as well) whilst chatting they will let you know the area's to pay attention to.
I have had a tour round thier place and at the time they were fabricating the frame work for 2 dragsters and building a 3000BHP Supercharged engine for one of them.
They have all the contacts for impotigng the Engines and boxes etc.
Deffo worth a chat with at least even if just to locate an engine.