Crazy how similar they are. A little history from Wiki...
The
Type A engine was
Toyota's first production engine, being produced from 1935 through 1947.
This engine was a 3,389 cc (3.4 L; 206.8 cu in)
pushrod,
overhead valve, 6-cylinder, three bearing engine copied from the 1929–36
Chevrolet Gen-1 3 bearing
Stovebolt L6 OHV engine. By virtue of a modified intake manifold it produced 62 PS (46 kW), while the Chevrolet engine produced 60 PS (44 kW).
GM used a number of local Japanese suppliers for the smaller engine parts (e.g. carburettors) while the
Osaka Assembly location was open until appropriated by the Imperial Japanese Government.
[2] Toyota was able to use the same suppliers for its cars. The parts were identical enough that pistons, rods, valves, etc. could be used in both the Chevrolet and Toyota engines interchangeably. There are several recorded instances of parts intended for one being used to repair the other.
[1]
The 3,386 cc (3.4 L; 206.6 cu in)
Type B was a more technically advanced version of the Type A. Production commenced in November 1938 with the opening of Toyota's
Koromo plant.
[5] The design was based on the
Chevrolet 207 engine, and built under license but with metric dimensions and minor revisions to suit the local market. It had a four-bearing crank and shaft-mounted rocker arms, as did the Chevrolet engine. The type B engine remained in production until 1956 at least.
The Type B was complemented and eventually supplanted by the similar 3.9 L
Type F which first appeared in 1951. The Type F is based on the larger OHV
GMC Straight-6 engine built from 1939 until 1963 in the same way that the Type A and Type B were based on the Chevrolet engines of their times. There was also an experimental 4-liter version called the
Type D.
