Just to follow up, here's what I did. Perhaps somehow this will help someone else down the line who is having a similar issue with a flickering shift light.
I re-positioned the light to mount on a bracket bolted to the intake and the light is now at the front upper corner of the left valve cover. Just lengthened the wires enough to reach back to the previous hook up points at the distributor. Power to the light is "ON" with the ignition. Pulses come from the "Dist" terminal on the HEI distributor cap. Since I had cut the wires short when it was mounted next to the distributor I added wire length and connected the wires with "bullet" connectors near the light so it could be removed easily.
Did a test fire of the engine and set the light setting down to 3,000, revved the engine briefly and the light came on nice and solid with no flickering. I do like the launch, recall and playback features of the AutoMeter light I bought and will probably switch to it later after a bit of real-world testing at the track. Thought I'd do a proof-of-concept mounting with the less expensive ProForm light since I had already shortened the wires.
Tomorrow and Saturday we'll be running the car at the Bootheel Fuel and Gas nostalgia drags at Sikeston, MO. For us it will be another test-n-tune opportunity but we might get brave and pick out a similar ET car to challenge to a grudge match. As always, if there are no puddles of oil or transmission fluid under the car, and it can still be rolled on the trailer when it's over, I'll be happy! It's going to be a hot couple days at 95-ish degrees so cool-down time between runs will be a bit longer I'm sure.
I also bought a digital tire pressure gauge. Glad I did. My dial type analog gauge from my circle-track racing days was way off. After I set the pressure evenly in the slicks, using the digital gauge, the roll-out was within 1/8" side-to-side. I think that's about as good as I can expect.
Lynn