Idle high

Unless it's a 360 with a 260 @ .050 cam there is no reason for it to idle at 1200 rpm.

If it's sized like a 403 voodoo or a XE268/274 it should idle at 800-900 max with a minor drop in gear.

Sounds like a vacuum leak somewhere. Power brakes? Makes sure it's sealed up well on the intake/carb flange. sometimes there can be a very minor interference which causes thing to not set properly.

Another is to disconnect EVERYTHING vacuum related from the carb, plug it off and start it up. See if the idle can be turned down and if the drop in gear improves.