Fiery , I ran up your donor engine , its not too bad , I got sub piston induction by mistake and made about 3 pistons to get the fit and 2 goes at lapping the cyl , , It just would not seal , the plane is about 1/3 finished , The piston is very thin and the conta piston has 1mm between the combustion chamber and the tommy bar screw and its hollowed out , With this radial porting it looks like the transfer charge just goes straight out the exhaust, I might try a real steep domed piston or deflectors on the piston top ,