Aggie-Jon,
I hope I'm not spreading misinformation, but I've always thought that a casting like your "B53" gives you the date of casting. B53 = Feb. 5, 1953.
Of course, that only worked for a certain 10-year period. I don't know what they did in 1963.
The 235 in my '48 had a B33 casting (Feb 3, '53). LAQ83376 was stamped on the flat spot behind the distributor. The head was B23.
My current 261 has an A241 casting (Jan. 24, 1961?) in addition to a 3769925.
That longer casting number will give you the engine size.
1948 3/4-Ton 5-Window Flatbed Chevrolet 34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.
