By all accounts, they are the same. I believe the original "B" was for bayonet base, but I cant substantiate that.
All plain designation 63 bulbs seem to fit identically with the correct incandescent amperage at 6V, so you should have no problem.
If you are going for a concourse restoration, then you will go down the incandescent avenue, however I have a faithful "driver" so am choosing to use (and seriously recommend that you consider) LED 6V plug/play replacements...check this link out and consider that (you can pick the temperature/luminescence color so you can get the right "look"):
https://www.ledlight.com/63-led-bulb-7-volt-ba15s-base.aspx If you go LED on many bulbs, contact me and I can give you the links to headlamp, interior, tail lamp, etc as I went through all that research/crossover stuff and could save you some headache.
I hope this helps. Dan M. (37 Senior Sedan)
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