You might need to look into a throttle solenoid as well?
I have mine idling with 16 degrees, 650 rpm, with the Webers and a 294S Compcams solid lifter cam. No solenoid. No vacuum delay. Vacuum can added to the A341 "Motorsport" distributor.
Shuts right off. 12 inches of vacuum, which is enough for the brakes and in this car all the vacuum level is a concern at all for. The Webers don't care how much idle is there...if any?
The 85 Mustang GT 302 uses a "Motorcraft" carb, which is actually a Holley and it uses the throttle solenoid.
I think I just saw one at low tide in my shop yesterday? IF it's there and not a mirage, you can have it to try and keep.
The 69-70 Boss 302 uses an earlier version of it. It might be easier to adapt to the Holley throttle plate than the "Motorcraft" version is?
They both have "unique" mounting brackets. The Boss set up since it is now a "rare antique" is expensive to come up with. The "Motorcraft" is available used on ebay but if you buy a new one is about $125.
The Boss version is easier to use and more compact.
I don't remember all of the solenoid set up details. I gave up on single Holleys sometime in the last century?
