There are plenty of genIII parts, they are just real expensive. I have a set of eagle heads 2 sets of early 5.7 heads, 2003 and 2011 injectors and everything to assemble an engine for a pickup or durango but the cost of the stuff to put it in something old is very cost prohibitive.

Oil pan
Headers, I can't find any manifolds to fit an early car.
Ign controller
Carb intake, even the crappy ones cost $500+ a decent one is $1000
EFI controler and harness, even if I use my 03 computer it is not cheap to set up.
Engine mounts
Engine accessories

I think I figured out a way to hook it to a 904 cheap (Jeep converter, 5.7 flex plate) unless someone knows why this won't work.

A 6.1 block is not needed for most guys, the line of site flow path the air takes to the center of the cylinder is not affected much at all by the smaller bore, look at the 2014 engine masters competetion for proof. They ran GINOURMOUS heads on 5.7 blocks and mopped up not just power per cube but low end TQ and all out HP were awesome. Even the Kass ferd hemi had bores about the size of a 273 and came in 5th place. Bore size is just not as critical on a hemi as a wedge.