DOT-5 can be run if there's NO natural rubber seals. I believe the seals in the slave in the rear drum are natural rubber.
I'd personally stick to DOT-3 or 4. You can get new cups for the rear brake slave at NAPA. Take the old ones out and the bore size should be printed on the cup, or take it with you and they'll match it up.
Make sure the bore isn't pitted too. If it can't be honed, then it's shot and needs repalcing.
“When the going gets weird, the weird turn professional....” ~ Hunter S. Thompson~
R.I.P. Rubberdown. 1971-2012