comment: I'm working on this right now for mine. I can give you a few pointers, but I haven't finished mine yet so ymmv.
  You'll need plate mount stabilizers.
  O-ring OD diameter needs to be approximately 195mm
  4mm o-ring width is too thick. I'm currently trying to find one around 3mm. Durometer selection is going to be pretty slim with these sizes. 
  I'll let you know what else I find out!