OK on second (or third) look at your photo, your bed is probably at the right elevation. Since you're doing a restomod, you could put the bed wood higher if you like. The bed would be shallower, if that matters. Stock bed would have the bed wood barely clear of the frame arch, and it looks like your shock mounts are higher than that, but hard to tell. You could definitely move them forward if room allows in front of the current mounts. You can probably find the original holes for the shock mounts on the frame web just forward of where yours are welded.
The original bed was supported on the cross sills, but it looks like yours may be supported on something welded to the front panel of the bed. Again, no issues with that, if that's the way you want to go. Originally there were three cross sills, one at the front panel, one just behind the shock mounts forward of the frame arch (missing on my photo), and one at the rear, which extends up to the level of the angle strips and forms a ledge for the bed wood to sit on at the rear. The center cross sill doesn't connect to the bed sides, but just supports the bed wood.
Again, you're free to do whatever you like with yours.
