Hi Nick
My old engine used a MSD 6btm and distributor and when I changed over to DTA, I think the Autometer was just connected to the tacho ECU output. We certainly didn't use the adaptor you mention.
My new engine will be using a Omex 710 and I plan to connect the same Autometer to the ECU output again - providing I can resist the urge to get a digital dash of course
Surely your ECU has an output connection for tachometer ?
Regards
Darren