The problem is solved. I did check the fuel pressure and it was exactly what it was supposed to be with no vacuum at the regulator. So after all these tests, everything pointed at the fuel injector.
How could it be a problem? I just had it serviced (cleaning and calibration) by RC Engineering in Torrance, CA. Anyway, I pulled the injector again and also found another injector at the local Pick-Your-Part, just in case the first one was Tango Uniform. I explained my problem to the tech at RC. He took the injector he serviced originally back to the test stand. Turns out the injector was stuck shut.
Evidently, injectors will stick if you don't install them right away after servicing. Residual cleaning or calibration fluid dries out and jams the injector. Since we had the original service done on January 29, the injector had almost two months to petrify. Also, old injectors will do the same thing after a period of inactivity if they get too varnish-y
Our tech said if I dropped the injector and installed it, that might've cured it. All he did was give it a couple of love taps while it was on the test stand and it started working.
That was yesterday. Today, I installed the injector, retested the resistance to make sure I had continuity, and the engine fired right up, settling into a high idle just as soon as I remembered to plug the wiring harness back into the injector housing. Oops.
Thanks to RC Engineering for fixing the problem so quickly. They're a really nice bunch and their work always makes a satisfying improvement. I was unaware of the sticking injector potential so the next time I do a motor, I'll have the injectors serviced just before the motor is ready to start.
The new engine is running beautifully. Very flexible as it will get the car moving from 5 mph in third gear with no pinging or lugging. Nothing like the torque of a brand new motor with excellent compression.
It's still a thrill to hear them come to life for the first time.