Sorry to be vague, guys, I didn't anticipate the level of interest. The car is a 2000 G-Force GF05 Indy car. It may have raced in the 500, but both teams that owned it over its life went out of business so I'm not sure.
You can see a picture of the engine compartment here:
http://www.apexspeed.com/forums/attachment.php?attachmentid=75513&stc=1
The Chevy emblem is on the rollhoop, the black X-brace is part of a sub-frame made to take the place of the stressed original engine, and the grey thing behind that is the bellhousing. You can just see the two silver rods coming into the picture which are temporary replacements for the coilover shocks.
I'm not set on any particular engine. I just need one that is short enough, has the starter on the engine side of the flywheel and has a clutch housing that is less than 8 inches in outside diameter. Those are the parameters that are hardest to change. Nice attributes to have after that would be a small diameter flywheel and a shallow oil pan so as to not rob any of the limited ground clearance.
I'll also look into the E15. Stoffregen Motorsports, I may have some follow up questions based on your past experience.