The drums on these trucks are huge and work very well when adjusted properly. You can replace the complete stock braking system very cheaply through sites like RockAuto. I don't know what your financial situation is, but completely new manual drums would work quite well if other priorities require the big bucks....and at less time and money than any conversion will cost.
Knowing I was going to convert to a Crown Vic front clip, I still replaced the wheel cylinders, master, lines and shoes in my 1970. For the year I used the truck before the changeover to CV disks, that thing had really great brakes and it was dirt cheap! For a 2WD that may only see weekend duty, they're more than sufficient.
Just my
![2 cents :2cents:](./images/smilies/icon_2cents.gif)