The following information was copy/pasted from the VanPelt website. This and other sites I used when rebuilding my motor (42 G six cylinder) is where I came to the conclusion I did.
The original G Series engine was used in Ford Special, Ford Deluxe, and Ford Super Deluxe passenger cars. It was also used in Ford Commercial and Truck models (except COE - cab over engine). The engine was rated at 90hp at 3300 rpm.
The first two years (1941 to 42) models used Holley single barrel carburetors (1GA-9510-A). The 1946 to 47 models used the Holley single barrel carburetor (5GA-9510-A).
In late September 1947 Ford changed the six cylinder engine to the H Series which had the same bore/stroke and displacement of the earlier G Series engine from 1941 to 1947. The newer engine had slightly higher compression and the new "Loadamatic" type distributor. 1951 was the last production year for the flathead six as Ford introduced the new over-head valve six for 1952. Other changes include larger main bearing journals, new rotor type oil pump, newer Holley carburetor (8HA-9510-A), new water pump, and one-piece valve guides. In early 1950 the camshaft was changed. Otherwise, the basic engine remained similar to the G Series design of '41 to '47. The block and head were of cast iron with the valves located in the block. The newer version gained 5hp over the G Series. The engine is easily distinguished from the G Series by distributor location....the new Loadamatic distributor is mounted to the left side of the cylinder block near the middle of the engine.