I'll admit up front that I have pretty much zero knowledge about what I'm writing, but just going on my 617 experience, knowing that the engines are pretty similar other than 1 cylinder.

I'm guessing that the earlier pumps are "M" pumps and the later ones are probably "MW"s. There are differences but Dieselmeken prefers to build high performance pumps from the "M" pumps because most of the adjustments are external. If your pump has an external ALDA it'll be an "M". At least on the 617, the quick and dirty way to tell them apart (they really look quite a bit different once you've seen both) is that the shut-off diaphragm is right up on the top rear of the "M" and is hidden down low on the rear of the "MW" and is hard to see at all.

Again, on the 617 they can be swapped for each other and in fact my '85 engine now sports an "M" based SuperPump. The lines all must be bent a bit and the shutoff line has to be moved as noted but basically everything will bolt up. If, however, you want a bolt-in this may not be exactly the way to go.

No clue if this is helpful but it's what I have to offer.

Dan