Hey, comgratulations on the new purchase! All 67-72s pickups (stepsides & fleetsides) could come with a wood bed in them, and fleetsides could also be had with a steel bed. The pickup most likely came with a wood bed, but there's no telling whether it's the original wood or not. I think the original wood beds were pine and they were painted, so if yours is a nice oak bed that's clear-coated then it's not original. Enjoy the new ride.
Ben