I saw a build recently that used” Roger Payne power” for 26 stock class. It doesn’t seem to be a secret, so I guess you could call him and ask about the engines.
I recently sold two RS45 EVO engines that were NIB for $480 each. I have one more new RS45 EVO but I pulled the head off and took the piston and sleeve out to look at it. I put it back together with a new C-clip and I will include some extra C-clips. $460 shipped to you USPS. Prefer Paypal.
This was purchased in December 2017. Today someone sent me a PM about it asking if it was the 2019 version so there may be a newer version that came out this year. I don't see anything on the CMB website about any changes for 2019.