[Rufton]

First I'd adjust brake shoes until they are starting to drag.
Then I'd pop top off mastr cyl (keep fluid topped off during bleed).
Then I'd crack each wheel cylinder and install a tube to see if each will gravity drain.
You can install a tube to wheel cylinder and reverse gravity bleed; full tube elevation higher than master cylinder.
Sometimes residual pressure valve or proportioning valve will interfere w/ gravity bleed; in that case you can bleed w/ a helper or pressure bleed.

If shop couldn't bleed they may have installed brake lines incorrect.