Brake problem

Are the rear brake shoes adjusted properly? That is very important on that car or you will have a soft or very low pedal. If you just replaced the rear brake shoes but did not adjust them then that is your problem.

Brake shoes are adjusted.

If the shoes are adjusted properly and the pads are good and the calipers are sliding properly I would say you need to bleed the system again. I would start by bleeding the master cylinder itself. To do that you crack the hoses loose at the master cylinder starting with the left front (blue) Let it flow a bit then gently push the pedal about 1/2 way. Once you're sure there is no air do the same with the right front (red). During the bleeding process do NOT push the pedal all the way down. Doing that can damage the seals because of dirt/rust in areas of the bore the piston doesn't normally reach and can give you a falling pedal or poor brakes.

Now once you have those two bled, bleed the front two calipers, then the rear wheel cylinders. If you still have a soft pedal watch the flexible brake lines as you step on the brakes, be sure one (or more) are not swelling up with brake pressure.