Actually, it was completely designed by Lotus. The only possible way you can credit is GM with any part of the LT5 is a) they owned a substantial part of Lotus at the time, and b) it was built here in America.

But everything else was Lotus Engineering in the U.K. GM bought Lotus in '86, and immediately used them to revitalize/revamp several of their projects - including the Corvette. They gave the mandate, and Lotus went to work. The LT5 would not have been possible if not for Lotus' innovative design: DOHC instead of pushrods, aluminum instead of cast iron, pent roof combustion chambers, etc. etc. etc.

I read that Lotus themselves rated the LT5 at well over 400+ hp, but had to detune it for American specs. Also, the thing that finally killed it was GM's ability to up the rating on the pushrod engine to above 300hp in their experiments of the early/ mid-90s, and their insistance at installing the ZR-1 "squared taillamps" on the base model 'Vette - to the fury of ZR-1 owners, who felt that the little badges weren't enough, they wanted a car that not only performed different than the base mode, but looked different too.

Sadly, Lotus is now wholly owned by an Indonesian company, making this kind of project unlikely to occur ever again - the cost of consultation would be too high. Too bad, too...