Pedal goes to the floor?

How are you bleeding?

I like "old" methods. I don't believe in vacuum or gravity bleeding. I believe in keeping positive pressure "in" the system. This means pressure bleeding, or by 2 people "on the pedal."

Have someone pump it up. Release starting at furthest rear cylinder, a hose into a container. CLOSE the bleeder before the pressure falls off completely and do not allow your helper to release the pedal before you get the bleeder closed.

If worst comes to worst, read the shop manual on checking procedures, which give some pressure checks

Buy some plugs / unions. This will allow you to pull the rear line loose at the rear axle and plug it, and temporarily eliminate the rears.

Master MUST be bled at the master first.

It's possible that "half" the master is not working. Have someone work the pedal. You should see "action" as it returns in both halves of the master with the cap removed.