Two answers: first, the rotary is frequently, if not similar to the OPS, ST, and other RISE engines. I sent a private message to Dankar asking for the deminsions which I can check with my rotary disk stores, sometimes one can be machined to fit, and sometimes the timing is identical as one Rossi and old ST were. The older STs had (sometimes) a rear cover that had a (pegged) false back that (can) be (repegged) to adjust the timing. I have some of those. All are the Updraft versions, but will work with CL or RC.
Second question, on the beast eBay, ANY new ROSSI will fetch a minimum of 300 to high of 500 Bucks, a sandcast, even more. I watch the sales frquently and can never afford one, but build from new parts I find around through a contact in Italy. Heavy, yes, as Dirty Dan told me a while back, "...sell it, throw it away, get rid of it!" they are no good for CL Stunt!