I would go with the extension ring because of the flexibility. It's one more o-ring, but with a vacuum system it's no big deal. I went this route with my M1mkIII housing, and I was also able to use the the 30mm macro. I sold the port along with the housing, so when I housed my OM-1 I went with a dedicated port for the 30mm and got the 24mm ring to allow me to use the 60. For me, the 30 is a lot more useful- faster focusing, more useable for fish portraits in crappy viz, etc., but I still have the ability to use the 60 for specialized shoots.
