Unfortunately there are no cheap, easy bolt on upgrades. There are some reasonably easy though. Options I'd look at:
- XT130 strut, RA60 hub and disc, MX62 caliper, a little machining.
- RA60 strut, hub and disc. Sigma lower control arms to fix camber. Live with the slightly longer steering arms.
- XT130 strut, Peugot disc, Hilux calipers. May be a bit heavy.
- FC calipers and DIY adaptors. There should be dimensioned drawings around for the adaptors you can make, otherwise I might be able to dig them up for you too.
- Custom bracket to suit any caliper you like. Unfortunately the hole spacing and shape of the brake mount on the AE86 strut is a bit weird, but anything can be done.
But even for one of the more simple brake upgrades, the price starts to add up once you include changing struts, discs, calipers, pads, maybe a master, etc, etc.
Hen