If you put anything in it but the BBC, you'll always wonder how much nastier it would have been. I say big block, and I'm a smallblock guy.
The muncie will handle it. The 4L60 would probably need some beefing up, and a converter. Instead of paying for that stuff, use the money for a ring/pinion swap and you're done. That would make for a pretty reasonable, but respectful setup. If you want better mileage stay off the go pedal. (yeah right
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