You can purchase a manual adjusted proportioning valve that is very small and hooks to the rear brake line only. You install it on the rear brake line just below the master cylinder. Run the brake line down the firewall and feed it between the inner fender and outer frame rail. Run the brake line down the outer frame rail until it is safely past the bell housing and feed it back over or through the frame rail to the rear of the car. Not a good idea to feed it under the rail as it will probably get damaged.