Accuride either bought or merged with Firestone at some point. I had some rims that were stamped "Firestone Accuride" (or was it the other way around?)

I think the 6 numbers are date stamps, as you suspected.

Can't find the 3sl8, 2la, or similar numbers in my catalogs. They probably have significance for just the rim portion before they were made into complete wheels.
I was thinking you would find a part number something like Accuride number "28157" But from looking at the Accuride catalog , page 55, the original part number would have been stamped on the center that was removed in your case.

None the less, I suspect they started with Accuride part number 28157, the 22.5" 6 lug Budd wheels desirable for late 50's and even 60's GMC and some Chevy trucks. Whatever they started with, I don't think they are very common wheels now days.
If you call Stockton to inquire about the different number of hand holes, see if they will tell you the original bolt pattern of your new wheels?

Thanks,
Grigg


•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-