No pressure in brake line

The right rear is farthest from the master cylinder and it takes along time to get fluid to pump to it especially with a new master cylinder.
To bench bleed the master cylinder, it should have came with a kit to do this, but if not get some short brake lines that if bent around will connect to master cylinder outlets and then cut off the other end so that it will reaach the bottom of the master cylinder reserviour. Then make sure the fluid level never gets low in any of the bleeding process. Now pump kind of rapidly at the master sylinder for a while and then pump it normally until there are no air bubbles coming out of the holes in the bottom of each reserviour.
Now to bleed the brakes you need to get some pliable clear tubing that you can get at Home Depot. It needs to fit snugly over the bleed nipple and be long enough to run it over something that will hold its highest point above the caliper and then run it into a plastic bottle or jug till the hose goes to the bottom.
Start bleeding at the farthest caliper away from master sylinder and work closer to it. So, the right rear first, the drivers rear second, right rear third and then the drivers side front.
Fit one end over the bleed screw and run the line higher than the bleed screw then into the bottle. Put a little axle grease on the threads and once you get some of the air out, you can just keep flushing fluid without stopping to hold and release and tighten bleed screw. Since you have so many issues, I would suggest flushing it until it comes out clean.
Starting at the right rear caliper, (This is the farthest from the master cylinder and needs to be done first.)Pump and hold but you can also just pump if the level in the master cylinder is dropping. It takes a while to get fluid going from such a far place especially with a new caliper. To create the pressure to get the fluid going, it has to fill a large cavity the the master cylinder is not designed for. The master cylinder only moves a little bit of fluid when you use your brakes. So be patient, it will come.
If the pedal gets hard to pump, there is contamination somewhere and is often in the bleed screw. Remove it and clean it out.
Now move on to the drivers' side rear brake. Then the passenger side front brake. Then lastly the drivers front brake.
This system of working farthest away from the master cylinder to the closest helps remove the most contamination and helps more fluid to move along.
ALSO, never let the master cylinder get below the low mark. That will pump air into the brakes. If you think bleeding the farthest caliper is hard, a master cylinder is a killer to bleed.

Well, since you have all the other calipers flowing, and I am assuming you have a setup like I described with the tube to be sure that there is no air in the line, then the master cylinder is bled. If I did not mention it one of the advantages of using the tubing bottle bleed setup is not only seeing the clear fluid but you can see that the air is not in the line any more as there will not be a bubble from the bleed screw to the highest point wherever you may hang the hoseto run down into the catch bottle.
If there were a clog you would probably, in almost all cases, a stiff pedal that will barely budge and no fluid coming out of the caliper. It really can take a lot to get fluid to that back line. I have built new brake sytems on motorcycles that took 20 minutes to get the fluid to the calipers. Now think of the volume in the line to the caliper. The problem is getting it to compress up against the air inside the line enough to slowly start moving in small increments down the line. You have to pump and hold, if I did not make it clear or mis-spoke, that you cannot keep pumping the peddle until it is free of air and moving freely and over the high point in the tube and this is after doing enough pump and holds that your helper is hating you for making them have leg cramps. Once clean fluid is flowing, you can just pump the pedal without holding and tightening the bleed screw so you can flush the line extensively. The last pump and hold, then tighten bleed screw and the line is done.
You are just going to have to keep at the pump and hold or get a vacuum hand operated line bleeder. They are helpful, but not a wonder tool. They can be helpful in your situation though because it is really hard to get that initial amount moving. Once that happens, it will flow like all the others.
Put in another 20 minutes on the right rear caliper just using the pump and hold method and then my suggestion would be to check the caliper piston for free movement. Brake dust and goo will sometimes build up on the piston if the dust boot is old and keep the piston from retracting all the way into the caliper. Unfortunately you don't have a way to push the piston out a little to see where the line of cruddy stuff ends and clean piston begins. Just start by spraying the piston liberally with brake fluid and use a rag or shop towel to remove contamination. Repeat until piston is entirely clean to as far as you can get it where it goes into the caliper. You could alwasy remove the caliper and attach another brake line to it to move the piston and make sure the piston is clean and there is not anything to keep it from retracting all the way into the caliper. Although you should be able to judge this by eye.
Although this would also show you if the caliper piston is moving out freely and does not have any leaks. If it has a leak, or moves crooked and that menas the inner seal is bad or failing, this will make bleeding a near impossibility as well.
Just hang in there and some fluid will come out sooner or later. It is odd you are having so much trouble when you consider that there is the old brake fluid in the line and it is not like you are starting a completely dry system. Double check the bleed screw by removing it and spraying some brake cleaner through it. Watch your eyes!
Let me know how it goes.

That is great news. Really good that he found the clog as the pedal will usually get really hard to push in most cases. So, that is good diagnosis work on his part.
I am glad it turned out well.

Take care and come back anytime.

Dr. C