Thanks guys. I've reached out to Gibson Support with some details - hopefully they can help me. I have spoken with others who have L-48's with flat backs.
This was advertised as an L-48 from the 40's, but I'm not so sure. There is no stamped serial number inside the back. The guitar is the same size as my 1957 L-48, however it has 1 less fret and it has a flat back (2 piece) which really threw me.