Jumping back momentarily to it not fitting the transom, I have the same problem of squeezing an aux in 'tween frame & engine on mine. I did toy with de - tanking a Seagull (tank being the wide bit) , and either mounting the tank on the A- frame or building a bracket to mount it lengthways above the flywheel.
Ended up just tilting the main up & to port out the way when using the aux! (it's now a lot easier to turn hard to port than stbd, coz when tilted up the tiller clouts the main instead of the back of the case...!)
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