Wheelbase and Utilty Beds

[Olden Days]

Ok I am thinking about putting a utilty bed on my 69. Do I need to find one that was built specificly for chevys of these years. Or is any 8 foot utilty bed gonna work?
The reason I ask is, I think I saw on here somewhere that the newer 73 up trucks had a slightly longer wheel base. If this is so would it still be the same measurment from the back of the cab to center of axle for proper wheel well placement, thanks...