"Street/Strip" covers a lot of territory. With the 6 speed I'm guessing you want to have fun driving it on the road. Weight distribution and balance is a lot better in an A body with a small block... preferably lightened. Lighter front=more fun to drive. An aluminum headed SB stroker would really work well in an A.

Of all the combos you are considering, one to avoid would be a stock stroke 400. It is hard to build compression and power with this setup. Worst of all worlds... heavy and lower power than a SB stroker plus poor parts support. If you do go BB, suggest 3.75" stroke minimum and lowdeck for fit.