considering the rectangle port heads I would go with a 454, Im currently in the middle of just such a project, the car is a 65 chevelle, 10:1 454, with the large oval port heads. I pocket ported the heads, and have installed 2.25x1.88 valves and shaved the heads to attain 10:1. the cam is a ISKY mega HDY 280, the intake is a weiand action+ (due to hood clearance) whitch I gasket matched and did some minor cleanup on. The whole idea was a stump pulling monster that he could drive to car shows etc.. the car has a 12 bolt, 4.10 gears, and 275/60/15 rear tires. Th350 and a TCI breakaway torque converter. this combo should pull like a freight train to 5800.
I will add photo's of this project soon, along with the performance.