All Bronco's were available with tow packages, you may or may not find one but they're not difficult to replicate. The standard gearing on the Bronco's is 3.50 so that's what I'd expect to find. Available engines were the 300-6 cyl, 302-8 cyl & the 351-8 cyl, the 460 was never offered in the Bronco but it's a common & popular swap especially for towing. They make excellent tow rigs (within their capacity) and your flatbed & BroncoII are well with the envelope for a full-size Bronco. If you *don't* find a tow package Bronco it's no big deal but but you will NEED to add an aux transmission cooler as well as the hitch & trailer pigtail. Occasionally you find a Bronco with the optional 3.08 gears but I haven't seen very many of them since, to my knowledge anyways, they were special order-only trucks.
Just for the sake of comparison I've always been a full-size fan and have a real love for the 78/79's. Now that I've finally gotten my $hit together I'm looking for another one to build with my sons, problem is they aren't as common as I'd like so I figured I'd have to go find one & tow it home. I also have 2 sons & a daughter who all want something more than a beat-up ****** to drive so between finding a 78/79 for me, vehicles for all of them AND the inevitable trips to go & drag home the half-finished car/truck that they just HAD to take out on a Saturday night. I knew that I was going to need a tow rig myself and found a cheap 88' Bronco with an automatic & 302 that will work just fine for everything I'll need it for. A 351 would have been nice but it'll be a daily driver and the 302 will work just fine for the towing I'll do with it, it's not like I've got a freaking gooseneck I need to haul. A 302, automatic tranny with aux cooler is fine for what most of us do. The 302's will haul 6600lbs & the 351's will pull 7000lbs. Not enough of a difference for me to go out hunting a 351 & to pay the extra fuel that it will use day in and day out.
Last year Roadkill posted a PDF of the towing specs, you can find it here:
http://broncozone.com/forums/index.php?showtopic=10920