Thanks for the replies everyone. I have an OS .40SF ABC I bought in the '80s that still makes impressive power and never "needs" messing with. I recently bought another.40SF NOS to pair up with my original in a twin I'm building. I love that engine but the .60 size NOS SF's are kinda rare now. There must be a good .60-.75 2-stroke currently in production right now I could be happy with. My 3 year old SuperTigre.61 ringed has been nothing but a dissapointment. I think I got a friday engine and its time to move on.

I'm also thinking of an internal tuned pipe so that may drastically limit my choices.