Get m/cyl as level as possible fill res. leave top off and try to get bleeder valve on caliper as close to 12 o'clock postion as possible , open valve and let it gravity bleed , keep res full , till fluid is coming out of bleeder. You may need to get fluid moving by stroking lever super slow. It may take some time. I'm pretty sure it's just air in the system. If you wind up needing a caliper I have a very nice one off a 96 only 809 miles on it with new pads.

Something plugged , seals installed in wrong direction, damaged bore , internally bypassing. Is the hose clear? Disassemble , clean , inspect , blow out ports with compressed air and try it again.

Before you do that, open the bleeder with the top off the master cylinder and walk away.
If the lever is pushing the brakes, the hole is closed, no fluid passes.
It worked on the bench.
What changed?

Takes a few strokes to get the pads out to the disk. If you are sure no air is in the system, close the bleeder and VIGOROUSLY apply the brake. The same condition that you created on the bench should happen.

You need new seals, not just seals that look good.

Yup - I'm hoping the master rebuild kit that came in today will take care of this problem.  I'll put it in tomorrow.  Good advice on checking the cylinder bore to be sure that it is not damaged... I'll eyeball that close tomorrow as well.  Hopefully good news will follow soon....

Success!  Put in the master cylinder rebuild kit... new seals.  Brake is good now, but did not take right off without some coaxing.  Here is what I did:
After putting new seals on the new plunger and double checking the cylinder bore to be sure it was smooth, I put the master cylinder back on the handle bars but did not hook up the brake hose to it.  I filled the reservoir with brake fluid and then pumped the brake lever a few times.
Fluid did not pump out of the outlet, but I was seeing some bubbles come up in the reservoir, out of the two small holes going into the brake cylinder.  I sealed off the outlet with my finger and continued to pump the brake lever slowly.  This eventually started to build pressure and fluid would squirt from my "finger seal"  Apparently getting some pressure built up expanded the seals on the plunger, which improved the seal and thus the pumping action.  I then connected the brake line and refilled the reservoir.  I opened the bleed screw on the slave cylinder and let a couple of reservoirs worth of fluid run out.  I closed the bleed valve and started working the brake lever slowly.  Got some resistance in the lever after the brake pads seated on the rotor disc, but it was still a bit spongy.  I opened the bleed valve again and let some more fluid run out, closed the valve and added more fluid to the reservoir.  After pumping the lever a bit longer, the usual firmness returned and the brake action was working well.  Apparently the old seals had worn enough to where they could no longer make a tight enough seal to build proper pressure.