Matt at DIYautotune "thinks" the IAC will work if wired only at the ends, ignoring the center taps - but cautions that since he hasn't tried it to make sure, I might have to use a 4-pin IAC. I've wired it that way, so we'll see what happens. I read 58.6 and 58.8 ohms per coil this way, so the driver should be ok since the GM stepper motor coils are 58 ohms/coil.

On to the distributor....... Charlie, I'm looking at powering the distributor's optical sensor from the ignition coil (+) to (+). I guess the ground will need to be a separate wire that runs back to the MS ground collection. Alternately, since I'm using a shielded wire for the Vref signal, could I use the Vref shield as optical sensor ground path? Do you see anything wrong with any of those options?

Frank