RE: Dago Red Mustang and a Jett 60 RE
I don't think you're gonna get a pipe anywhere inside the fuse...at least not without serious re-arranging of practically everything inside...not practical.
I have one, w/ a Webra .50 and Ultra Thrust muffler...nicely balanced combo and surprisingly fast for that size engine.
If you want to use a rear exh. engine, you're most likely going to have to get or make a custom header, and put the pipe down the C/L of the belly. The header will need a substantial drop.
I could eyeball mine and give ya a WAG if you want? (very ) rough header measurements, just out of curiosity...