I'd suggest abandoning the original 'bolt ons' and use the more modern ones.....The Challenger vintage accessories appeared to have been orphaned a while ago and I think you have found out they are hard to find and priced as such....and there are very few that are unique to crusader.
I dug thru my library and found a 'before 1980' factory manual....looks just like the parts you can find in the online factory parts lookups. If you are only swapping the one engine for the time being, you can 'save the bolt ons' for the other one, until its time comes....just food for thought....