Mounting Thermoquad to air gap style intake. What adapter?

Joe,
Congrats on using the excellent TQ. Use the Holleys as a weight on the trash can lid to stop the wind blowing it away....
You say strictly street use. If usable power is to be 5500 or under, then the Performer is a better choice & no spacer/adapter is reqd. Bolt on deal. Be realistic with the rpm expectations, which will depend on cam & other parts. Nothing to be gained, only losses, fitting a 6500 rpm intake [ the RPM ] on a 5500 rpm engine...
Because the carb pad is lower on the Perf, you may be able to add a 1" spacer [ divided or 4 hole, NOT open ]. This often adds a few upper end hp, with no loss down low. A free lunch...