engine swap
If you really want to do it differently, go with a slant six and find some of the old factory hot parts for it. In the early 60's, mopar made factory headers and 4 bbl manifolds for the slant six, as well as a couple of optional cams. That would make a true retro rod as well. While the slant sixes came with some rather restrictive valves, even a little porting and a good 3 angle valve job will really wake those heads up. The 225 slant six with 4 bbl from the factory was rated at 196 hp @ 5200 rpm and 212 lb ft torque @ 4200 rpm, so it was some what of a high winder. And this was with 8.2:1 compression.
That is compareable with a lot of the small V-8's at the time that were 40-50 cubes larger.
You might also want to check with Clifford Performance, they are 6 pack specialists.
An afterthought, the last couple years the slant six was in production, they had opened it up to about 240-250 cubes if memory serves me correctly. That was in the late 70's early 80's.
While the 400 etc would definately be a tire roaster, I fear that your early drive train might not handle the strain of that much torque. At any rate, I would recommend going with an automatic, as it will be decidedly easier on your rear gears. etc.
