As
@DirtDonk has said...the answer should be interesting.
Your 76 big bearing housing end is not compatible with the Explorer pattern. The explorer pattern is the same as the Torino big bearing ends, which some people call the "medium duty" big bearing housing. And yes, the bolts are 3/8 diameter, instead of the 1/2 inch bolts that you have. Both ends are nominal 3.15 diameter bearing.
Worse, the brake offset for the Explorer is 2.5 inch. Your brake offset is 2.36 inch. So you would need custom axles in order to have the disc brake hat land in the right place.
In my case, I had new custom 35 spline axles made...so I got to choose the brake offset. You will also need a spacer to fill in the excess thickness difference between the drum brake backplate thickness...and the disc brake caliper mount. It's about .200 inch...but don't quote me on that. Currie Enterprises used to service that spacer as a component, but last time I called them...they wouldn't sell them. (Wilwood sells an extended retainer that does the same job...but it isn't nearly thick enough.)
Because of all this, I just bought a USED wilwood big bearing big bolt 9 inch 2.36 disc brake kit in 5x5.5 lug pattern. I don't think I'm going to use it.