Try cracking a bleeder screw and pushing in on the brake shoes.

I know you said the M/C rod is non-adustable, but somewhere in the mechanical end of things you should find a way to adjust brake pedal free-play.
Perhaps an eccentric if the pedals are firewall hung.

You need about 1/4" - 3/8" of free-play (pedal at the top via the return spring) then push the pedal and it should travel through the free-play and start pushing the M/C cylinder and applying hydraulic pressure to the brake system.

Looking from here, there's a chance you don't have any free-play at all, the hydaulic system is lightly pressurized and the brake shoes can't release - or back off - all the way.

Another one that happens with lack of free-play is the M/C port that supplies 'make-up' fluid is blanked off and can't replenish the fluid in the M/C cylinder proper.

Arcing used to be a part of all brake jobs done at brake shops, but they quit doing it because parts quality was high back in the day and it was deemed not necessary for most brake jobs.
The brake shoes wear in pretty fast, so I wouldn't worry about arcing them.

Is the drag factor so high you can't rotate the wheel by hand?
If it's just a little extra drag, go ahead and run them.
Doesn't take them long to break them in.

Don't sweat the break-in procedures either.
Just drive the car normally and the shoes will wear-in just fine.

Swapping shoes from side to side could tell you a lot.

Take a look at the box the shoes came in.
Made in China?
I've been hearing some interesting things about the poor fit of wheel cylinders bore to piston clearance.
Like in "way too much" clearance.