Well you do have a title for the bike I assume it is registerd an insured ,So that rite there would say that those numbers are legit , The guy maybe rite about the VIN stamping on the cases they did use diffrent style numbers on some years with flatheads and Pans and if I remember it was the number 4 and 6 that had variations the 4 would be either closed or open at the top and the 6 was as he stated to you staight back or curved I dont remember the years and what stamping should look like on your year, but I know I have the info in my garage somewhere ,I will dig around for it, but I would suggest maybe talking with the guys at the hydroglide forum , the belly stamping might give you a clue also, or if you could track down the prior owner and ask if the OEM cases were blown and got replaced with aftermarket one and then did a re-stamp, but if that was done there should be some other numbers there but most likly on the inner of the cases. I bought a 57 basket over 10 years ago from a guy who got it from a guy who got it from a guy who said he had the title , but he got it from a guy that never gave him the title this was a 25 year old basket case , It took me over a year to get the guys name who said he had the title and he gave me another name , I have a friend in Law enforcement who ran the guys name and came up with address .Well to make a long story short I got intouch with the guy and he was happy to help me out he got a new title and signed it over to me costed me a few bucks paying for all the fees and some extra for his troubles it took almost 3 years to get the title , The motor is done just sitten on the bench when I decide in the build I want I will proceed but for now its a Basket but with a title, So what I am saying you might have to start investgating the history of your bike and you will find all the previous owners will be happy you got in touch with them