I have made several conversion heads and they all worked very well. I simply made a blank head with the contra piston the same size as the original combustion chamber. I used a viton o-ring to seal it and a fine thread cap screw for adjustment. Davis fuel was the easiest to come by and it was a concentrate that I mixed with scented lamp oil. The smell was still so strong I gave up. In my opinion the fuel (kero, lamp oil etc) was worse to clean and keep on the outside of the model. Even after running all the fuel out and plugging the exhaust and carb the smell inside the van and garage were just too much. Good luck with the conversions.

Dennis