OK I have done a search in the fuel section with no results. LOTS of look see but no answers. I have a 1977 F-150 2wd with a 19 gallon rear tank. I have the opportunity to get a new 1976 Bronco sending unit. My question is ... will is work in my tank . My sending unit needs to be replaced and only has a 7/16 feed line.. I do not believe this is enough to feed a major modified 400. I have already installed a new Holley mechanical fuel pump so I am not going to replace that with an electric one. Any help ?

 

77 F150 2wd 19 gal and a 76 Bronco (rear metal tank is a 12 gal (?) and the side tank, under the dvrs side seat, is about the same size and plastic). So I do not either think one form any early Bronco 66-77 will work.

 

And it's not likely you'll ever find a discussion about that exact subject because it's not common practice to use pickups/sending units from the wrong tank. I take it that it's hard to find the one for your truck then?
Where does yours mount? Mine mounts to the horizontal top of the tank and the Bronco sender mounts to the front vertical side.
You said "7/16" fitting, but you probably meant 5/16" instead? The two common sizes are 5/16 and 3/8. A 5/16 fuel line will feed up to 350 modern horsepower. I say "modern" because they're a lot more fuel efficient than our old gas pigs ever were. I'm thinking you'd want one with a 3/8" feed for a V8, but you say it's got the smaller one, correct?
Do you have a six-cylinder engine? Or did yours just come with 5/16 for some other reason? Maybe it was replaced with the wrong one in the past? What size is the rest of your fuel line? All the small size? In rubber, plastic or metal?
Which engine do you have? Might be time to upgrade to the 3/8" size and make the rest fit. What size inlet is the fuel pump? Seems like mine was 3/8 all the way to, and including the pump inlet. Maybe 5/16" outlet to carburetor though.

Oddly enough, the rear main Bronco sender does work in the front aux tank of a Bronco in a pinch. The were different units from the factory, but before the side tank was available we were using the rear sender and it actually worked even though the rear was 11gal and the side was 7gal on most years.
A 77 Bronco rear tank holds 14 and is a plastic tank, but I believe still mounts in the vertical front surface. Here's what they look like: https://www.wildhorses4x4.com/produc...nco_Fuel_Tanks

Have you looked at all the usual suspects for a proper replacement? Graveyard? LMC? Scott Drake or Dennis Carpenter? RockAuto even? No luck?

Good luck. But like 77&79 said, a standard 66 to 76 EB sender is likely not going to work.

Paul