with alot allready said.

Compression is the key. Use 915 or reworked 516 heads at a minimum or look into aftermarket.

Stroker would help, but it will still have the same problems if the heads aren't changed or looked into. The problem seems to be piston choices are really slim. DO NOT believe the charts from the piston makers because more often than not their piston will sit too low.

I am pushing right at 400 with 2.14/1.74 ported 516 heads, Comps nostalgia .474 cam, Holley SD and a 650 mighty demon. Not a stroker here. All in all I am happy with the mill. Its got great low end and has great idle, and drive quality. There is probably more in the motor That I may try to find later, but for now it is just fine for cruisin around town.