$1000 is wayyyyyy too much. $500 is the most you should spend. The dodge version I the NV will bolt up to the D300, but you'll prob have to buy an adapter BH.
I got my NV4500 from a guy in Texas (on eBay) who does nothing but rebuild transmissions. He custom built mine, a GM model with the lower first gear and a dodge tail housing. I didn't need any adapters because I bolted mine to a GM motor. He puts all brand new bearings, seals, and syncros and even the upgraded 5th gear. All for $1300 shipped to my door. Good guy, I'd do business with him again.
He also had a bell housing for me and could probably get whatever you want to. I used the internal hydraulic sale cylinder on my setup. Good luck!
'77 CJ7, LS1, NV4500/D300, Ford 8.8, 4" of lift, 33x12.50 BFG ATs...