RE: BTE Delta Vortex and Jett muffler help
Sounds like you have it worked out. Outstanding on the balance without adding dead weight to the tail. It will make very pretty landings if the CG is where the book says. Looks like the space shuttle coming in; nose high, slow, under control.
The OS91FX, even compared to Jett or Nelson. is a suprising package of power. I've had all three on these Delta's and the OS is my favorite for several reasons. And initial cost is NOT one of them. The OS is a very powerful, light, high power-to-weight ratio, good running engine in the exhaust and prop configuration mentioned above.
Let us know how your package turns out. It will be interesting to follow your progress. You'll have a lot of fun with it.