Bed Swap/ Gas Tank Problem

[yoopone]

New to the forum today. I have owned a 1976 long bed for over 25 years now. It has been a victim of pretty bad rust but it is all restored. I installed the 3rd bed of it's life last winter. The bed came from Arizona and it came off of an 85 I beleive. It had the side mount gas doors. Truck has dual tanks. When I bought the proper filler necks to match up to the filler neck mounts I quickly discovered the original tank inlet neck is a smaller diameter. So I need new tanks. My question is will my current fuel pickup/sending units swap over from my 76 era gas tanks to the newer era tank with the 1 5/8" inlets? Any help would be appreciated!