I've never seen one like that. Obviously not stamped at the factory because it is so uneven and different fonts. All the factory replacement engines I've seen have the first 3 digits (engine displacement like 228, 236, 248, etc) stamped and the rest blank so that the end user can stamp it to the same number as the original engine in case that number was used on the truck's title.
The casting number list over on
OldGMCtrucks.com says 6107328 is used on 53-54 248 blocks, but I just realized that list doesn't include any 248 blocks earlier that '53. The 228 block casting number is shown as the same for 39-53, so it could be that your 248 casting number is correct for all but 1955 248 engines.
Have you found the casting date on the block?
