The front panel, rear sill and all the cross sills are wood floor specific. The front panel extends further down to support the wood under the front edge. The rear sill also has a ledge to support the wood. The cross sills are shorter in height to allow for the much thicker wood (0.81" vs 0.06"). The bedsides are interchangable between the two as are the wheelhousings with a conversion strip kit. Went over this earlier this month, you might want to look at that thread and also buy Mar-k's conversion manual.
http://67-72chevytrucks.com/vboard/s....php?p=6067480