That's not a bad idea. I'll give it a go and then shoot him a PM.
I think you are 100% correct. Moving that big mount to the outside wouldn't get the spare anywhere near where it is supposed to be. I think the big mount stays in the bed and the part(s) I'm missing go on the outside and attach with those big bolts with the spacers.
I'm going to try to mock up a block that functions out of wood and then see if I can find someone to fabricate it out of metal. I'm also going to look at the parts book a little more. There may be a whole other piece like the block I'm missing (8.350-4) that mounts to the outside. The one in the picture doesn't have holes in the back for the grommets that I think marked up the bed.
The piece is probably similar to this, but with a different bolt pattern for the lug spacing:
Thank you much!