Definitely wouldn't put more than 4 inch stroke in a stock block.

I would likely buy a rotating assembly from Rod on the board here(BPE), nice stuff and he has great customer service.
What is your intended power level?
Keeping it at 600 horse or less will contribute to long term health with the stock block.

69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight
418 BPE factory replacement headed stroker, 565 lift solid cam
Best so far, 10.40 @127 1/4
1.41 best 60 foot
6.60 at 103.90 1/8