28oz is the way to go. You can balance it to 50oz, but will require a lot of drilling on the crank - makes it look like swiss cheese!
Stick with 28oz for your application. This comes directly from Tom Naegle at DSS.
I took my entire stroker package (rods, wrist pins, pistons, crank, alumimum flywheel, Fluidampr, etc) to Fowler's Engines here in Columbus for the balancing. They also said 28oz was best for my 331.
Hope this helps.
E
BTW - if you get an aftermarket fly, it should come with weights in 50, 28, and 0 increments for balancing purposes.