Looks like you bought that Van that was on Craigslist in Portland. Is that the one you are working on?
When you bench bleed the MC, read the directions carefully. There is a certain length of stroke, and do it slowly, that is important. You may have to bench bleed several times to get the trapped air out. Sounds like that's the problem. It's more difficult to do when you have a 2 compartment MC. Takes two people to bleed the lines, apply brake pressure, open bleed valve, pedal to the floor,hold there, close valve, let up on pedal, do it like that until no more air is seen. Use a clear tubing into a jar with a little fluid in it so you can see when all the air is out. If you can't get any fluid out at the rear, it's possible that the hose to that brake is collapsed inside, or the valve is plugged with dirt/rust, take the valve all the way out and make sure it's open. If the brake fluid is old and brown keep bleeding the lines until clear fluid comes out. Just make sure you keep the MC full of fluid or you have to start all over again. Takes normally a quart to flush the system.