[Christ]

The rabbit P'up engines are turds, they were never designed to do anything more than haul groceries and pets around LOL.

Just about any small diesel engine will have plenty of torque to get you where you need to go, including some small equipment engines, like Bobcat and Hyster (Hyster mostly used Mitsubishi 2.0/2.4 gas engines).

Depending on what you want to haul, you may be able to find an older 40 HP 3 cylinder Suzuki snowmobile engine, which usually produces lots of torque down low to keep the sled from bogging down, and are a popular swap for trikes, even though they're gas, and not what you're asking about.

Almost any engine that is small enough to fit in your engine compartment will work though, and bolting it to the tranny is a matter of making an adapter plate - which you're already familiar with.

I'll put my nose out there and see what I can come up with as far as possibilities for you to look into though.

I do wonder what type of problems you'll run into w/ the S-10 being OBD compliant though... You (obviously) won't be able to run the stock ECU and sensors, and may have a problem with emissions crap trying to make everything work if you don't have an emissions based engine (would technically have to be at least the same OBD rating as the chassis, preferably newer.)