Hey Kenny, you know this Youtube channel EricTheCarGuy ?
If you'd figure out what parts you'd need to install disc brakes on your van....possibly a supplier would send them for free if Eric would do a video on the brakes swap/install.
He's a 76 Ford Fairmont owner/fan so he might really 'dig' your van too (he is in Michigan though I think).
Maybe it would be possible to work out a good/fun deal for everyone.
If you could get a deal with a brake parts supplier and would send that to Eric he might be interested and give you a good deal...
Just dreamin'
Anyway, good luck with your cool 74 Ford Econoline !