Straightforward to do - get a CSP disk brake kit in wide 5 format and away you go
If you are prepared to go for Porsche brakes several options open up or you could go for a late bay setup and fit later wheels
I run a CSP kit with a remote brake servo and Wide 5 wheels
My 71 came with discs/servo as standard so you might want to check that either your bus is actually 71, or if someones fitted an earlier/aftermarket beam and/or spindles with drums?
I kept the 71-72 discs but bought new latebay calipers with the bushes to adapt them to 71 fitment. Calipers just needed a little grinding to clear the hub at the front