I made about 10 sets of rear brakes in the early 80's using front calipers, a custom hat type disc, and custom brackets. No handbrake however with the stock front calipers, and now I need the handbrake to keep the Authorities happy
Line lock is not allowed for an E-brake, but with a bit of work I could use separate spot calipers, or maybe easier just to get a new more modern system. Bigger wheels will allow me bigger brakes.
I already have a proportioning valve on a stock MC. My rear end is stock Tiger.