Without knowing what pistons you have right now, There were several options, I' say look around online for a piston and sleeve set of original fire crator pistons.
I put a set in my super C when I rebuilt it along with a few other slight modifications and it was almost double the PTO HP. It dynoed at 30 once I broke it in and took it to work to try it on the dyno.
You have to get the proper distributer shaft and advance springs for the firecrators and it is all still available at the dealer. Well, it should be at a good dealer. These originally came in a boxed set with everything you need for the conversion. You can still find them if you look around.