RE: Diamond Dust Kit
With a rear intake engine you should be able to get away with a smaller diameter crank that is easier to spin [than a front intake type]. Checking the disk valve timing from a known world class rear intake engine like the OPS .60 series ought to get a OS.46DF right up there with the best...especially if Nelson made upgraded parts for this engine.
The one comment that Dave Shadel made that sticks with me is that the "modular / bolt together" case design seems less trustworthy than the one piece type.
A big obstacle for me would be to learn how to service [or modify] the rear intake valve.
A bigger question would be why MB/Profi decided to use front intake when they decided how to build the most powerful .40 in the World.