I replaced the master cylinder. I did the bleeding on the new one on the bench and lost almost no fluid during the installation. The brakes feel fine. The master cylinder is way above anything else in this brake system. Since the small amount of air is at the top of the lines where they enter the master cylinder, will that air bleed up through it as it did during the bleeding on the bench and ultimately leave? Or do I need to go through the total bleeding procedure which somehow forces that air all the way down to the wheel cylinders and out?

You will probably be fine, but, to do the job properly, you should bleed the whole system. It's an easy 30 minute procedure on a truck. Bleed in this order: RR, LF, LR, and RF.

Be sure to tighten both lines going into your master cylinder with a flare nut wrench.

I'll probably do it shortly. However, my Haynes says RR, LR, RF, LF for these trucks.
It is hard to go against the word of someone from Texas regarding old trucks, chuckle!

Thanks... Skip
Born and raised in Texas

Come on home, Native Texan, where you belong. We won't hold it against you that you moved to San Diego.

Since you have a split braking system (RR and LF on one circuit, LR and RF on the other), you bleed the furthest wheel from the master cylinder (RR) then the LF. Afterwards, you bleed the next furthest wheel from the master cylinder (LR) then the RF. That's the logic behind it.

Hey Tex... Perhaps, it's different because it has disc front and drum rear. One master cylinder circuit holds twice as much fluid as the other and one brake circuit line to the master cylinder is larger than the other. I assumed that one circuit is for the front and the other is for the rear. What'cha think, now? It's a Bendix type one
Master cylinder. Thanks... Skip

The disk and drum configuration does not affect the two standard diagonal braking circuits. Automotive engineers want you to have one front and one rear brake, on opposite sides of the vehicle, in case something happens to the other circuit (e.g. a caliper, wheel cylinder, or brake line failing). It has been done this way for at least 60 years.

Hey Tex, Apparently this is another way to do it. I have found sites indicating the disc, front, brakes connect to the larger of the two chambers on the master cylinder while the drum, rear, brakes connect to the smaller of the two chambers on the master cylinder. This kind of makes sense because the drums are always adjusting, thus not needing a lot of fluid replacement from the small chamber, and the discs do not adjust but keep drawing additional fluid from the larger chamber. By the way, I was an engineer, too.

Best... Skip