I think you'll have a lot better luck finding a 454 than a 427.
I just bought a 74 C10 with a 454 (complete with rod knock) for $550. I'm gonna use the front suspension and a buncha the other parts on my 64. I'm gonna put the 454 motor in the corner of my garage and rebuild it for my race car...maybe a coupla years down the road. I plan to run the 406 in the race car for the next 2 seasons.
The bellhousing should be the same pattern between the I6 and the "twin 4." But I dunno if I'd wanna trust a Saggy behind a rat motor. I'll have a fresh TH400 for sale, but since you're on earth and I'm in Utah, I'm not sure it's possible to ship stuff from here to there.
hth,
