Hi Ryan,
Yes, Mar-K (
www.mar-k.com) sells replacement wood kits for these years and that's where we got the kit for dad's truck.
Unfortunately, you need a lot more than just the wood to convert from a steel floor. The cross sills are not as tall (since the wood is thicker) and the rear cross sill (at the tailgate) has a special notch to accept the ends of the boards. There are also about 9 special steel flange pieces that bolt onto the bedsides/wheeltubs. They bolt up to the same holes in the bedsides/tubs as a steel floor and serve to make the transition over to the wood.
During the restoration of dad's truck, we had to replace most of those special parts due to rust. For the cross sills, we bought some un-drilled 67-72 style ones from Mar-K and drilled them to the 73-80 bolt pattern using one of the originals as a template. I modified a steel floor rear cross sill (did a bit of cutting/welding to add the notched area). And we had a local sheetmetal fab shop make replacements for the perimeter flange pieces using the old rusty ones as templates.
The bedsides, wheel tubs, tailgate, and front panel are the same as used with a steel floor.