[Lynn Eades]

Really you should be looking for a T214, a T215, or a T223 engine for your ambulance. The T214 is correct with a 3 and 1/4 bore and a 4 and 5/8 stroke (all these three engines are the same at 230 Cu.in.They all have 8 bolts holding the flywheel to the crankshaft. These 8 bolt cranks have extra counterweighting to run at governed revs for long periods (to suit a hard working truck)
The T215 was from a half ton WC dodge and the T223 was from the WC62 and 63 6x6 Dodge. These engines are great engines and are very reliable.
I would make sure the water distribution tube is in good condition. It goes into the block behind the water pump and delivers a good flow of water to the exhaust valve seat areas.
The 4 and 6 bolt crankshafts are generally from cars and light duty engines.

The bigger block engines are in the same bracket, being a very reliable engine of that post war era.
The bigger block engines will require modifications with regard to the radiator. either a new rad. with different tanks or moving the original forward which I consider pretty ugly. Just my thoughts.

On the Diffs, there are two sizes of driving heads one (8 1/2"?) mounts on a 3/8 dia. stud the larger, later diffs mount on a 7/16" stud. You have the small one. These were improved as time progressed. Your one pictured, being the weakest, with the cast carrier, triangular holes, and had two spider gears.
They made a stronger carrier(still 2 spider gears with round holes in the carrier) and then the third one which was heavy duty with 4 spider gears.

As you said, the half ton axles (half shafts) were smaller dia. so the up grade was to change the side gears to take the 3/4 ton axles.

A note:Many of the gearbox internals are interchangeable with the Ford 4 speed truck box.
Nice project! Keep posting.