I've used L&M several times....excellent work....even cerakoted the milled area to match the slide, in this case FDE.
Here's one he did for me. This particular mill job replicates the factory cut in the Walther PPQ's, enabling me to use all the factory/stock adaptor plates. I forget the cost, you'll just need to contact L&M.
C&H Precision just milled my .45 for the adapter with built in rear sight (which they also installed). They did a great job and were reasonably fast. They're also Walther approved. I had L&M mill my 5in M1 for an adapter plate & they also did a good job but I'd go with C&H. Primary Machine also rocks. I had them do my P10c. Milled the slide plus camo cerakote. Very fast and very nice work. Can't comment on their Walther work if they do it tho.