Brake lines plugged or both rer wheel cylinders bad?

[65ChevyC20]

I recently picked up another 65 C20 that hasn't run for a few years. I swapped out the master cylinder, single circuit, which I did bench bleed before install. I crawled under the truck to bleed the right rear and couldn't draw any fluid through. I was using a vacuum pump and then switched to pressing the brake pedal to see if I could get fluid back there using the old method. Still no fluid at bleeder.
I switched over to the left side and got the same results using both methods, vacuum pump and depressing brake pedal, and still no fluid.
I then moved up to the front end and was successful at getting the brake fluid through the front brakes. This truck still has drum/drum set up.

I then went back to the rear brakes and opened up the left and right bleeders and still couldn't get any fluid to flow. I then closed off bleeders and opened up the brake line where it splits to go to the left/right drums and I could force fluid out at that point.
I'm at my wits end here. Is it possible that both rear cylinders are bad? Or a possible plug in the lines after the splitter.
After putting away my tools I decided to see if I could spin the rear wheels, both were locked up. Not sure if this is rust on drums that is keeping wheels from turning or not.
Just want some input before tearing into this truck again this weekend

Wheel cylinders are $14.00 bucks each, not a big expense, if that is the problem

[PGSigns]

My 65 was that way when I got it and I put all new wheel cylinders on it. The moisture in the brake fluid settles out into the wheel cylinders and the rust quickly. I replace them on any old truck I work on that has been sitting. I also swap the front hoses and flush the lines. Just good to know it will stop like it should when needed. Never have seen a set that did not need replaced.
Jimmy

[VoodooCLD]

I had this problem last weekend. Put brand new wheels cylinder on all 4 corners. Still couldn't get the rear to bleed. I ended up pull every brake line connection from the master cylinder back and blowing them out with air. It turned out the rear brake hose going to the rear axle was super plugged. Couldn't even poke it through with a steel rod. New hose solved that problem.

I'd buy 4 new wheel cylinder, 2 new front brake hoses, and the 1 rear brake hose. It's cheap insurance for a single master cylinder system. Not sure if you've done these before, but the front wheel cylinders require a deep 1-1/8" socket and a stupid long breaker bar to get loose.

As for the wheels being locked the emergency brake could have been pulled for a long time and the cables are seized in the "engaged" position.

[61K10]

you need to pull the drums and look at things. I would replace all wheel cylinders if setting that long.

[Jimal]

I had a similar situation with my K10. Flushed the hard lines and replaced the rubber lines and the wheel cylinders before I got the brakes to work. I also replaced the master cylinder, the brake booster, the drums, the shoes, the hardware and a few of the hardlines while I was at it, if that makes you feel any better...

[VoodooCLD]

Yep, the fittings on the hard brake lines are usually seized to the line and will twist and pinch the line when you break it free from the wheel cylinder. It may be worth pulling all 4 brakes and wheel cylinders at one time, that way you'll know how many hard brake lines you need before you go to the store. Don't ask me how i know.