Looking great, my friend @j-healy!
Net profiles show RLM65 undersides too commonly and I read a few discussions (which, as usual, end in speculation). I believe our friend @tcinla has a strong point there. RLM63 (greenish gray) would be a suitable underside color once the top camo would be applied, so, the too much of a hassle of painting the undersides at the field could be avoided. I also believe that from B/W pics you cannot really tell if the underside is RLM63 or 65. And yes, I believe they would have used tape to obtain a hard edge, but that does not mean that the undersides were painted RLM65.