[olddog]

On the block, the groves from the H beam rod strike is most likely below where the rings run with the 3.78 stroke. However when you stroke it to get 471 that may not still be true. This block may be fine for the original stroke, but not for a stroker crank, without major expenses. Maybe you can run a 3.98 stroke, but not a 4.125 stroke.

You could be better off with a new aftermarket block and sell this one to someone needing original parts for a restoration project.

I hope my random thoughts might be helpful. I feel your pain here.