There are still options. Getting a Tohatsu 3.5hp or Mariner 3.3hp would be a good auxiliary. You might even get away with short shafts given its location.
I used to have a Zodiac Pro with a Yamaha 40hp main engine and squeezed a Tohatsu in. You have the advantage, as the Pro had a lipped transom.
Now the decision. Fit an adjustable bracket, and quite honestly it will rattle like a toolbox in a Vauxhall Viva. It be tempted to see if you could get something like this fabricated but with a far shorter stem box section. Over-engineered maybe, but it's not going anywhere.
I'd also ratchet the engine when it's in the up position. With a stainless steel U-bolt on the deck.
Is that with or without VAT?