[Tom Goldman]

There is a huge benefit in air flow with the larger bore size although I would go to 4.600" ,the additional .025" would be insignificant .
I would go with the 4.250 stroke and a .400 long rod. ….This has proven to be a good combination for making power thru a very wide RPM band .
On a car as heavy as yours , you will benefit from the 2 1/8" headers even with the larger displacement.
Just don't over cam it with too much duration .