I have a 77' and put new tires & wheels on this Spring. The 76/77 models have a little closer tolerance at the front kunckles. I'll explain below, the best set up for a 76/77 model running 35-37" is 17" wheels with 3 1/2" of back spacing.
After a bunch of research and looking my experience is that the 17" wheels today are the same as 15" wheels were for the past 30+ years. When choosing rubber over 33", tire selection is very limited for 15" wheels. The trend is for larger and larger diameter wheels. That said, go with 17" and you'll have an unlimited choice of tires.
A common change today is to move the tie rod's to the top of the knuckle, TRO. This does a couple of things; it moves the tie rod up about 2-3" for better parallel alignment between the drag link and the trac bar -better driveability, plus obviously because its move up it allows for better clearance when off road.
However doing the TRO conversion also make the tie rod closer to the wheel, -kinda.. This is part of the reason to go w/ 17", more clearance. Generally speaking, when using 17" wheels everything just fits nicely.
And a lot of "modern" rims are made with 4" or more of back spacing...in other words this sets the wheel more inside -terible for a Bronco. You want a stance that offers stability, you want to take full advantage of a tight turning radius, and the tires can stick out to be parallel with the fender flares. You'll want to use the stick-on type of balance weights inside the wheel, not the [hammer-on] type that attach to the outside of the wheel.
Here's a pic of a 76/77 front end using old style 15" wheels and hammer-on type of wheel weights, TRO conversion. Notice there isn't much clearence between the wheels at the rim & weight. Another option is to use wheels spacer's
http://www.wildhorses4x4.com/product/Aluminum_Wheel_Spacers_Kit_Blue however there is no reason to "have" to use spacers if you buy the correct wheels to start with.
And here is the same 76/77 front end with 17" wheels installed with 3 1/2" of backspacing. Notice how much room you now have.
Here is the tire/wheel package that I went with, looking close you can read 37' x 12.50 x 17. In hindsight, and knowing what I know now I would have choose 35" rubber. 37" rubber is just a little too big, 35" is the perfect size. At some point in the future when I buy tires again I'll be getting 35" rubber
And here's a shot that shows the stance you can expect using 12.50 wide tires, and wheels with 3 1/2" of back spacing. These are the old style rigid fiberglass flares. Many of the newer style flares stick out just a little bit more. With this stance the tires stick out just a tad bit past the flares....some states have strict rules on how far the tires can stick out and/or mud flap requirments.