...if you really want the big hp and a long-lived engine, go with the bb*. One of the locals here on the Cape has long said that "the closer the cubic inches are to the horsepower/torque figures, the longer the engine will last between rebuilds". I've been juggling between rebuilding a 351 Cleveland and going with a 406(?) stroker. Clevelands rev like air-drills and I decided (for the time being) that under 500 hp/ft-lbs was sufficient. C. 450-480 in a 2670# Butler is streetable and shortshifting yields good mileage on 92 octane! A cross-Cape friend with an ERA has a 427 monster---must have 575+ hp. He gets appreciable mileage by short-shifting the Tremec and rumbling around under 2200 rpm---but he's got to add octane booster every refill and is looking at a potential rebuild frequency of 25,000 miles. That's okay, since he doesn't drive it a lot. I'd stick to and swear by the old adage of "there is no substitute for cubic inches".
In fact I am contemplating the same thing you are. Big hp and (maybe) big block---especially feasible in a Butler, with the engine about 18+" behind the front axle. It's really a "front-engined mid-engine" cobra.
Good luck.
*hope this doesn't start the old "fling-poo" discussion!
