Since the rotating assembly is pretty much the same price from 440 540 cubes , IMHO the bigger you can go the better. I am betting Fast68 suggested the 505 due to it probably working with an internal oil system. If you are willing to go external pickup, I would chose a 535 combo, 4.5 stroke and 4.350 bore. 10/1 compression, good flowing small port heads and a solid cam similar to the 590 mopar cam. A 950 will leave power on the table. I had good luck with a ported tunnelram with a pair of 800 holley dps on my 535 with 906 heads. Those carbs may not have been ideal, but the point is a big motor needs air! It went 10.50s at 3400 lbs and there was a fair amount wrong with some of my choices in that build 40 years ago. I ran those numbers with 4.10 gears and 33x15 slicks. Shifted at 5700. If i were to do it again it would get fuel injection on that tunnelram.