For posterity I'll update this....the sheet metal behind the headlight buckets are not the same on round beam vans vs. square beam vans. If you try to fit a round beam into a square van, it will sit ~inch or so too low and ~inch too far to the outer edge. Also the retaining spring on the corner will not line up.
It could be possible to put some new holes into the square van sheet metal, or just graft the round van's sheet metal onto the square.