BLUE actually used to make an adapter to fit Gefell capsules onto 451 bodies but they stopped making those a long time ago and I've been looking for a used one or pair ever since.
Gefell was the only manufacturer using the SMS system and only Gefell capsuels will fit onto Gefell mic amp bodies.
Yes, the MV690,MV691 and MV692 are all SMS. I had a pair of the M582 tube mics modded to SMS specs so I can swap capsules onto them as well.