The 1959 389 motors are known to have thick walls. They can be punched beyond 0.100 with block filler.
A 455 has a stroke of 4.21 inches
Aftermarket stroker cranks give you 4.25 inches of stroke, or about 0.040 more. You can't exactly just choose a piston, and expect it to work.
Lets go back to the beginning.
What year pontiac block will you be running?
Do you still want it to bolt in like the stock 336?
1959
yes- bolt right in
