Rik - is a wealth of information. He has seen so many applications with surface drives it's scary!!!
As far as slip goes, you got to be under 10% with big wheels like RIK suggested turning them that slow?
The bigger diameter the prop the slower it can turn to be efficient, small props need to turn faster to keep up.
As far as weight goes, the old Buzzi boats we ran plus the SH's with the diesels where naturally stern heavy because of the weight of the engines /drives. Our fuel tanks were in front of the engines and the longer range tanks were in front of the cockpit. With the diesels side by side there was no room in the engine bay for fuel tanks.
My guess is with the added weight you need the tank in the front of the engine room like we had ours.
RIK is right they lift the stern pretty good. We ran the SH's with straight bottoms no different than your Baja and they were fine - again your building a pleasure boat, it will run good for what it is I have no doubt.