The beech used for this plane body isn’t something I’d recommend for a plane sole (soft), really chewed up and the mouth is a couple of miles too wide so I needed to do something about it. I could slather it in epoxy (which I’m probably do anyway), impregnate it with resin, laminate on a slab of nice hard slippery wood (which I have), plate it where it matters or add a metal mouth closing block ala HNT Gordon. For whatever reason, I decided to go the plate route with a ~1/4″ brass plate. One advantage is that I will be able to cut the mouth in the plate, then install it. Which means the plate needs to be installed dead nuts square to the [aluminum] blade bed. Which turned out to be nontrivial as the body is nicely rounded and I had only three references: the top, the bottom and the blade bed. So I indicated off the front of the bed (through the mouth) and, with a tap tap here and tap tap here, dialed it in. Hogged out most of the waste with a big router bit followed by a 60° endmill.
I had previously cut the complementary dovetail on the brass by turning the plate upside down and using the same endmill.