RE: Engine of Aurora 25
I built an Aurora 25 in the late 80's, as I recall these are actually made for a side exhaust engine with the pipe external & just passing under the wing on the left hand side.
I used an OS 32- it's a perfect choice. Yes, the Jett would be stronger & probably "cooler" but the OS is very adequate for this model. Hatori used to sell a side exhaust header that had just the right twist to run the pipe in the right way...that may be hard to do. If you can find a set of MK 20 size retracts they are worth the effort to install!
I probably had more fun with this Aurora & Joker 25 with a Webra 32 & retracts than I did with the 60 size stuff back then.