RE: Weston uk working on Mini MagnumR prototype
I've got a couple of project drawings that might help, but there's no substitute for having an engine in your hand to size things up with. I just attack the model with a "rasp bit" on a die grinder when it is time to clear the exhaust, then glass the gaping hole back up after the model is built. It helps to have a 1/2" thick balsa sub-firewall behind the plywood.