Yep, easy upgrades.
1. Just a new stock EB motor will likely wake up your heater at least a little bit. After almost 50 years in place, it's likely getting a little tired.
2. There is a full-size Ford truck blower and fan (squirrel cage) that is an upgrade in size and flow.
3. The Chevy upgrade is a tried and true option.
I believe that both of the larger upgrades will require you open up the hole for the motor and cage to fit your stock heater plenum/box. And not sure about the Ford, but the GM motor requires a separate ground wire too, if I'm not mistaken.
The stock Bronco motor has two wires, while the GM only has one.
Simple as attaching the old ground wire to one of the attaching bolts, but it's something that has to be taken into account for things to work.
ryan97, it might just be that the wiring or the switch or the fuse box itself has too much resistance built up into it after all these years, which is what's blowing the fuse. That or the fuse is under-rated for the heater.
Most do not experience any trouble with that circuit. If you do, then you could update your wiring harness, or add a relay setup to take the load off of the switch and fuse, and put it all on the relays and their new fuse.
Any of the above is a pretty good improvement though, over a tired old motor and wiring.
Assuming everything else in the system is working as expected too of course.
Paul