I would suggest using the Ford/Lincoln 460 for the easiest swap. Mine would spin the tires on a 68 one ton flatbed with a six horse gooseneck trailer using the C6 automatic. I kept regular gas in one tank and premium in the other and only had to switch to premium to prevent pinging when pulling hills even with 10 1/2 : 1 compression ratio. I don't think the 396 would be that compliant.