8 3/4 disk vs drums

Since you have nothing the Dr Diff rear disk kit is hard to beat, especially if you add the 13" front disks.

Tires go a long way to help braking too, so plan on looking at 17" and up because the 15" stuff is 1980's or older for compounds and design (and way overpriced for that giant wiggle wort side wall), 16" you can get some better stuff but expensive, go to 17" and the world is you oyster.