...the thing i find troubling is that the serial number on the pillar and the physical paper title have the same number
That's a very good thing, if they didn't match then you'd be in trouble.
Without seeing the truck my guess is someone swapped the vin tag from a 54 onto the older truck. It's an old truck, very common for parts to be changed around, make two trucks out of one, replace damaged or worn out or rusted things. Could be a 54 chassis with older cab (original wrecked or rusted), and they liked the frame mounted gas tank and swapped it too. Without seeing details like engine mounts, frame and such it's hard to say what really happened.
Just call it what it is or resembles most, which sounds like a 48, no one will bother what the registration says so long as you have the legal title to it.
On edit, I missed this and your most recent guess at someone just noting the wrong year seems the most likely..
