Ok, you have a Japanese/ Canadian (rail) 2wd bed. It is available in 2wd and 4wd sheetmetaland short and long wheelbase. The american bed (no rail)) is only available in long or short wheel base. They only make one style american bed, 2wd and 4wd is the same.
This is what 4wd fenders and an american bed look like and it shuld give you a little more reference.
IMO stick with your 2wd sheetmetal.