We have a 3.3mariner 2 stroke Auxiliary for our 7-man
Zodiac (main is 40hp Mercury 4 stroke) and use the demountable
bracket and dovetail plate mentioned earlier (I got mine
via Duncans in Glasgow). The bracket easily fits in the bow locker
and the engine clips on the backrest of the 2 man jockey console
we have on our boat. To use the reserve you have to drive the engine fully up and hard over before mounting the bracket and engine. Bit of a fankle in rough water and slight restriction on steerage to s'board but perfectly usable. Pushes it along about 5kts.
I'd be interested to see a picture of your set-up, especially a rear transom bracket shot.
Regards the jockey seat - I appreciate this is probably the sensible option for negotiating a moderate swell and remaining in control, however I have a young family, and part of the deal was providing seating.
I wouldn't contemplate fitting a jockey seat now as there will be tell-tail screw holes on the floor. Probably just upgrade boat in a couple of years. My ideal craft is a Zodiac 550 Open Pro with Yamaha 90HP.