350 TBI, w/ bolt ons. (L05 crate) Running EBL

Engine starts up just fine, but when the RPMs come down after a second or two it dies. I can keep it running with the skinny pedal and drive it around and it's smooth and has power but dies as soon as I push in the clutch and take my foot off the gas.

Actions taken:
New cap, rotor, wires, plugs
Inspected IAC, it's clean and I can see it move in and out as expected when running.
Checked TPS reading
New MAP sensor
Remove and service distributor including new pickup coil and ICM
Haven't been able to find any vacuum leaks
Tried two different ECMs.

The computer wants to give the engine ~20 degrees timing when idling, and it does (confirmed with timing light, temporarily set idle speed to 900 where it ran long enough to check).

The kicker is if I disconnect the EST bypass it idles. If I manually give it that desired 20 degrees of timing at the distributor with EST disconnected, exact, same timing the computer wants to give it with EST, it idles fine. Return base timing to 0 and hand control of the timing over to the ECM and it doesn't run.

Anybody have any ideas to throw out?

 

I thought base timing was supposed to be 6 degrees BTDC, are you actually setting it to 0?

 

Definitely should be 6 BTDC on the 350 TPI, but I believe TBI is 0?

 

Ah, right. I'm not too familiar with the TBI so I can't say for sure. How old is the harmonic balancer? I've heard of the outer ring slipping and giving false timing results, but I'm just taking shots in the dark now. I'll leave it to those more knowledgeable than me in these matters I think .