Shaft length for spare engine and use with dinghy

All, I'm hoping to buy a spare engine for my Bayliner Classic but I also want to use it in a dinghy if I can.
I know that it's normal to use a short shaft engine in a dinghy and something with low HP, 3.5 approx, but will this
be any good for a backup engine for the Bayliner? Also happy to go with a long shaft and just loose some power in the dingy.
I have a spare engine bracket mount for the bayliner.

Thinking of getting this; https://marineparts.ie/3d-tender-world- ... ht-21-kg./

Is there any way I can merge the two, if so, how do I know what length backup I need for the Bayliner?

What length is the bayliner?? You would want one hp per meter of boat anyway for an aux engine,, id imagine it would be too small,,, might be fine for a dinghy though,,

Hi, boat is just under 6meters. So I'm going to need a dinghy that can handle a 6HP engine?

I was hoping to get an inflatable dinghy that could fit on the boat and I could blow up and go on shore with for visiting islands.
Sounds like getting a dinghy with an engine that'll do what I want for both might be tough.