Ford made 190hp 460s and 235hp 302s. Big Broncos aren't that much heavier than little ones. A piece of sheet metal doesn't weigh anything. I don't think there is 500# difference, honestly, especially on an older Bronco. A '90's Bronco is 4,600#. My B2, with the mods listed, is 4,200 and I have the certified ticket from Cat Scales. The empty weight of an early Bronco is barely 3,000#. I'm guessing a late-70s Bronco is around 4,000 even.
The problem is that people are incompressible. When you get a pile of truck parts together, you can pick up any bit of it. I have removed beds, cabs, frames, engines, axles all by hand. A big B scores minor chunks of weight here and there, but people still ride in both and in the end, the vehicles aren't that much different. The 8" wide strip of sheet metal required to make a Ranger into an F150 weighs a couple pounds. People are the same height and length so it's not like F150 occupants need a cab that is larger by the cube.
With both engines running well and of similar technology--the 460 big B will kick your ass.
Both engines built