Given that one or two have expressed an interest in the possibility of using their Pentax 645 lenses on Mamiya 645 bodies, it seemed sensible to start a thread dedicated to this topic.
Though Mamiya makes some excellent lenses in the M645 mount, there are many users of Pentax MF cameras currently without digital options. If you're thinking on switching to Mamiya in the absence of the 645D, it would be nice to keep all your existing glass, at least at first. There are also several outstanding Pentax 645 lenses that simply outperform the Mamiya equivalent: the FA 35mm f3.5 Pentax is perhaps the best example:
Review and lpmm data hereZörk in Germany has investigated the possibility of making an adaptor, but aborted their plans because they weren't happy with the rigidity of the resulting product: the registration distance is 'only' about 7mm. I've also started down this line, but spent an interesting morning with my lens repairman today investigating other avenues.
At this point, it looks like a reversible mount conversion could be done relatively cheaply (ie, less than $200). In some ways this would be more satisfactory than a very thin adaptor, though I haven't ruled out the possibility at this point. Either way, I should have some Pentax v Mamiya tests available soon, so we can tell whether the game is worth the candle!