Thank you very much for the very detailed answer, exactly the kind of insight I was hoping for and one of the reasons I love this place. I bought this over the internet as a titled numbers-matching motor, which I suppose it is. When I got it in person I was in the middle of working on another bike and just put it on a stand, this was a couple of months ago. Had a little time this week and started looking it over, noticed the later style timken bearing/primary mounting area, then busted out the third-edition Palmers and now we're here. I have no reason to suspect anything has been altered, BN area is just dirty doesn't look messed with to me, neither does the SN boss...which leads me to think the guy replaced his cases and had them stamped to match his title...I've reached back out to the guy I bought it from to see if he can shed any light, but it was a "posting for a friend" deal so we'll see what comes back. It wasn't a shady transaction or anything, and it's 100% on me that I didn't dig deeper. I'm a little bummed that it wasn't advertised for what it is but not bent out of shape by any means...pan motor with a clean title is still that, and I wasn't trying to do a resto or anything. At this point it'd just be nice to know as much of the story as possible, if for no other reason that I will want to be up front about it when and if I move on from it.If the left case is H-D it’s 55 or later judging by where the inner primary would go. Sometimes a replacement case may have had its SN done with factory stamps consistent with the original style but I don’t think it happened on this occasion. For example the F for 48 usually has more difference in the length of its horizontal strokes. And it may not even be a Harley F because some other characters such as the 4, 8 and 6 may be AM although they are similar to H-D types. Has the number boss been altered or is it just the photo making it appear that way?
Here’s an example for comparison of some characters. NB: there can be some variation in the appearance of H-D characters due to how they were struck.
Left BN is not consistent with factory stamping for a 48 Pan. Hard to tell what sort the 1 is but the 4 appears to have a serif across its base when I’d expect it to be sans serif. And its top looks open instead of being closed courtesy of a very short horizontal stroke. Notice the 9/6 is a straight-back style instead of the certain round-back type used for 48. (H-D used several types of round-back 9/6 in BNs over the years.) Anyway, why do you think your left case is not H-D?
Here’s a 48 Pan BN for comparison of some characters.
If the R-H case is H-D it’s 58 or later because it has no generator cradle. Its BN looks the same as the left BN and that is not good. I won’t be surprised if the BNs were done with some of the same stamps as the SN and it happens sometimes when people start with unnumbered cases or after the original numbers are removed. Is there any sign that a previous BN was removed from either case?
Pan R-H cases had a relay bracket boss for 48–64 but part of your boss has been removed and it may have been done to accommodate a magneto. Notice the timer clamp is secured by what looks like a tappet guide screw from a later model. I imagine you’ll eventually replace that screw with a stud?
On top of Pan cases H-D used at least two 7s: seriffed; and sans serif. First 7 was seriffed and it’s the only type I’ve seen so far on 48 Pans. I’ve seen both types for 49 and 50 but at some point during the 50 model year the sans serif 7 seems to have taken over completely. Your 7s are sans serif and their backs are fully curved as I’d expect but I don’t know if your 7s are authentic and the answer to that may depend on what happened with the BNs and SN. Also notice the area with the 7s appears level across both cases. The factory began machining that area as of 58 models to accommodate the regulator bracket that was used for 58–64.
Which Palmer book do you have? In his 37–64 SE he says the 7s are 1/2” tall. I don’t have the TE (36–65) but I know it says the same thing. On top of rear mounts I’ve seen hundreds of authentic-looking 7s, some seriffed and some sans serif, and on 41 Knuckles thru 70 Shovels, but none of them are 1/2” tall. I do not know why Palmer says they are.