Paging Mr. @imaoldfart, please pick up the white courtesy telephone!
I'm curious, and have been wondering this a while, but this seems like the perfect place to ask.
OldFart - the plates that keep the sear in, they look almost exactly identical on the p99 and the PPQ. Other than the hole where the striker extends out the back on the p99. Are those interchangable? YES And would that have to be done, on a project like WhyNot is talking about? I can't speak for what WhyNot was thinking, but I was saying you can simply swap a complete P99 slide onto a PPQ frame. So, all the original slide components remain the same.
ALSO curious, since WhyNot's problem is with the stipling, could a frame from one of the clones, like the DR99 Or SW variant work with the p99 slide? I'm thinking so, since those companies pretty much did use the p99 slides.
Walther made ALL the frames, so, I'd be of the opinion that the slides/frames are interchangeable. However, ALL these pistols have pretty much the SAME flat sided grip like the Walther P99....nothing to be gained with this swap.
WhyNot- the P99c is a fantastic subcompact, get it!! Here's why! https://www.waltherforums.com/forum/p99/111288-p99c.html