Very good info, Mike. I have 040 casting heads that have the threaded boss above #1(or#4) exhaust outlet so am using a GM 1/8" MPT sensor. The threads are close enough that it will work, and it's a closed hole so doesn't need to seal. It just needs to make contact and stay put.
I plan to also incorporate some extra ignition advance control into the warmup and idle control, hopefully that will work without an IAC.