Some things i noticed about that flathead engine:
* I think the flat head says "着火 1243" [FIRE 1243], which is a different
firing order than the modern 4-cylinders. Or is it? If the distributor turns in reverse, it is the same order, just in reverse
* It is fitted with an alternator, which does not match the 1950s type engine in the photo. Alternators weren't used until 1959, and not common until 1962-1964
* Is it an aftermarket head? All the ones I've seen before are cast iron, with the water outlet on top of the head. This one is much thicker, with water outlet on the side, and spark plugs sunk down from the top
* it has a floor shift transmission, which makes me think it is from a
Datsun 110 sedan, which used an Austin 4-speed
It may be a
Datsun D-10 engine (1952-964), 860cc -- 60mm bore x 76mm stroke. Very undersquare, as were most engines back then. With a 6:1 compression ratio it made 20hp. With a high-compression head, what do you think it made, maybe 30hp?