Hi,
My 2 cents, don't do the rear disc. I've been running rear disc for years, they stop the Bronco but the parking break sucks. I think properly functioning rear drums would be much more reliable and drums don't warp when they are too hot.
Good luck.
Another $0.02, after the fact, from me:
Properly adjusted rear drum brakes are more than sufficient for the type of driving conditions we generally see with our Broncos. I have installed countless disc/disc setups for customers who elected that setup against my (asked for, in this case) best advice.
This includes "daily driven" Early Broncos with 35" tall tires. The thought process that leads one to determine that they NEED disc/disc is often flawed. With the actual issue relating more to insufficient engine vacuum; failing "soft" lines (the brake lines going from the front calipers and/or rear drums to the hard line connection); old, sticking wheel cylinders; etc.
For under $200 in parts, and a respectable three hours of labor, you can completely "rebuild" rear drum brakes with all new parts and new parking brake cables. When you properly adjust them, you will likely never have to do the job again for as long as you own your Bronco.
There are benefits to disc/disc in certain situations and environments: when regularly pulling a trailer and when living in rainy climates, for example. But, for the vast majority of street-driven Early Broncos, my opinion was, and still is, that disc front/drum rear brakes will prove the better combination.
If engine vaccum is your issue, or you just want to avoid that altogether, then hydroboost is your answer. BUT, still with disc front/drum rear for the vast majority of us.
The whole "you need 4 wheel disc brakes" argument reminds me of the "Four Core Radiator" and "High Volume Water Pump" fads from the early 90's. Both became the "you must have this to solve your problem" reply...and both were wrong.
Again, my $0.02 probably too late, since you already purchased the kit.
