AHA. THERE are the responses I was looking for.
Curmudgeon- You're probably right about the bike engine. LOTS to go wrong. There isn't a LOT of space in the car, but if the fuel tank was relocated, it would free up some space. Not much, but some. Complete VW drivetrain might be doable... wouldn't have to go mid-engined. I'm not stuck on a midengined setup. I acknowledge that changing the engine location tweaks with how the car was designed, and at that point, all bets are off. Chevy Sprint sounds interesting, though not as powerful as I'd like...
50eggs- Sorry to depress you. Subaru... with a VW transaxle... RR config...
SVreX- I hear you. What I'm trying to avoid is "upgrading" by adding lots of aftermarket parts. More aftermarket means more penalty laps. I enjoy creative thinking, but right now, there are more options than I am able to consider, so I'm bench racing. And brakes are a whole 'nuther subject...
Silver- I don't know about Fiats "jacking". I know a couple iterations of the Triumph Spitfire were known to jack pretty spectacularly in the rear, probably what you saw. Anybody know if the Fiat does this?
Trans- Its rusty, but not THAT rusty.
HiTemp- Okay. I'll take your word for it. If it ain't engineering, it ain't engineering. The performance value IS abysmal, valuing the engine alone is what I'd be building toward. Wiki has the turbo'ed Metro 3-cyl at 73hp and 115ft lbs. If nothing else, parts wouldn't be too tough to come by.
EDIT to add:
Knurled- I had seen that, very impressive. Not sure all that's within my budget for Chump. Not sure how well that kind of setup would hold together in an enduro either... That may be another vote for VW power though.
/edit.
Keep coaching me, fellas. I'm not set on any one idea yet, so I'm very open to advice and suggestions. Thanks for the thoughts so far.