Brake proportioning valve

There is no one proportioning valve. Some models had something similar in the rear circuits, particularly Eldorado, in that era. I think that the proportioning is accomplished either in the master cylinder, or the EBCM. What type of concern are you experiencing, why do you think you need a proportioning valve?

Bleeding with the engine running is not necessary, but not problem causing either. Is the brake warning light, the red brake warning light? The right rear wheel hard to turn, does it become more free when the right rear bleeder has been opened, as if perhaps it is retaining some pressure. If I am not mistaken, the red brake warning light can only illuminate under circumstances of park brake indicator issues, or fluid level(sensor) type faults. I would also speculate, that if there was a proportioning issue, it would be a front/rear balance issue, as opposed to an individual wheel hydraulic issue. Keep in mind that the park brake is integral to the rear calipers, so if opening the bleeder screw provides no freedom, it could be an issue concerning the park brakes influence on a caliper, it could also be a frozen caliper.