A couple of other notes, the rules state maximum compression ratio of 10.5, considering that a 427 High Riser was higher than that, do you think that would eliminate the 1x4 High Riser 427, or could the compression be reduced? Or do you think the rules mean actual compression ratio, rather than factory advertised CR?
Also, since all the factory 426 "Street Hemi" and Race Hemis had 2 4 barrel carbs, and available cast single 4 barrel intake manifolds are required, does that exclude entering a 426 Hemi engine? Although the race Hemi came out in 64, with 12.1 compression and 2 Holleys, and the Street Hemi came with 10.5 CR and dual Carters, in 66, the only single 4 barrel 426 Hemi I am aware of, was a 65 NASCAR Hemi, which I believe was never offered in a production car.
As far as small blocks go, I would think the 340 MoPar would be pretty strong, although a 302 Z/28 engine could be pretty stout as well. maybe a 327/350HP too. Since the Boss 302 didn`t come out until 69, I don`t think a SB Ford will be a player.