Oh!! Good question, never heard that one posed before. I'll pass on the h.p. per cube aspect of the question and focus, instead, on what would look coolest for the project.
T-Bucket? I might go with the Boss there, a nice mix of old and new(ish).
Cobra? I'll go with the FE Cammer, always a good choice for most Ford product's but not necessarily all.
I'll never get around to building another car, but if I did, I'd really like to do a 64 Thunderbolt, I just love those lines. In that case, I'd have to go with a classic FE though and neither of the above.
In any or all cases, you could certainly build more h.p. than you could handle!
