Are you perhaps getting suffixes and prefixes mixed up? The "A" prefix (comes before) denotes a 16th series engine. "B" is 17th series, this pattern following all the way to 1954. Yes, I agree that AXXXXXB is a 1938 engine with forged camshaft.

You need a non-channeling grease. I highly recommend Sta-Lube SL-3303, a moly disulfide grease fortified with graphite. It's a CRC product. I'd clean all the old grease out of the unit first before replacing with a different lubricant. You may also want to replace the filler plug at the base with an alemite fitting; just add grease on occasion until you feel it coming out of the vent on the top of the case.

You didn't say whether the 1950 casting date was on the cylinder head or the engine block. If on the cylinder head, this is pretty common as cylinder heads occasionally required replacement, and spare parts continued to be made. My 1948 Custom 8 had a cylinder head with a 1951 casting date. But if it's on the block, it almost certainly indicates a replacement engine. I've never seen an authoritative piece of Packard literature instructing dealers how to deal with engine numbers on replacement engines. Nor do I have any credible evidence of how, if at all, replacement engines were numbered at the factory. If I had to guess, it would be that factory new spare engines had numbers within the original sequence; I say this because the range of engine numbers for a particular year and model usually exceeds the number of cars built and thus I conclude the additional were for parts inventory and already numbered. For example with the 1939 Six, 24,350 cars were produced but 26,040 engine numbers were assigned. So if you truly have a 1950 casting date on the engine block, and a correct 1939 engine #, the only conclusion I can reach is that a replacement motor was obtained, and the original motor number was stamped on it.

The engine # you gave is relatively late in the series, how does that compare with the vehicle VN?

B-1501 thru B27541 for the Six; B300001 thru B319537 for the 120, B500001 thru B506023 for the Super 8, and B602001 thru B602497 is the data that I have for 1939. I'm unsure what the suffix "A" means.

And incidently, Packard did make a Six in 1950 and thereafter; for taxicab service, for sale to White truck for their small series of trucks, and then just a bit later they also offered a marine engine based on it.

I believe they are from one of the pre-WW II Standard (320 ci) or Super (385 ci) 8 cylinder motors, the ones with the aluminum crankcase and cast iron bores. The roller followers are attached to pivoting arms, part way up each is a hardened steel pad which pushes the lifter up. I wouldn't say anything for these engines is exactly plentiful, but they are rarely needed for a rebuild.

Your float may or may not be set too high, but the faltering when the vacuum tank fills suggests you've got a vacuum leak somewhere. Have you put a vacuum gauge on the intake manifold with the engine running? If so, what kind of readings do you get?

Especially on Packards of this vintage which didn't come with factory-installed oil filters, one often finds that subsequent owners have removed the pigtail connecting the main galley output to the cross-block galley, and inserted a filter in series with that galley. Lousy idea because (1) the filter input has a flow restrictor, and (2) if the filter plugs, you essentially cut off the oil flow to the lifters. Not too bad if you have mechanical lifters because prior to 1938 the small 8 only used mist lubrication for the lifters anyway, but with a later engine with hydraulic lifters the consequences will be expensive.

A friend just bought a set of Diamond Back radials for his senior 1941 Packard. The carcass is Chinese-made, though I believe DB backs them with the same warranty they give to their other tires.

288 and 327 cylinder heads are interchangeable (though with a change in compression ratio). So perhaps the head on your engine was changed for some reason, or perhaps you don't have a 327 engine. Just check the engine number to ascertain this.

Gee, I've never read anything about any "correction factor" in the resistance oil pressure sending unit and would sure like to see the original citation for that. Are you sure you're not thinking of the restriction fitting at the inlet to the oil filter, which is after the oil pressure sending unit?