I'm confused, my 39 GMC bed is also 48" on the inside but according to Mark-k it should be 45 3/4
The following is from Mark-k web site, I used a 39 chevy because they only list a long stepside for the 39 GMC.
" Selected Make: Chevy
Selected Year: 1939
Select the Model of your truck bed: Choose ModelShort Stepside
Short Stepside: Length of bed wood 75 7/8". Inside width of bed 45 3/4"
Long Stepside: Length of bed wood 85 7/8". Inside width of bed 45 3/4"
I assumed when I measured my bed somebody had put a 40 bed on it at some point.
