Just swapped off all the computer stuff for Holley VS and Edelbrock Performer. If you put on the heater there's nothing. Is something not connected?

 

Your air flow is probably all going to the defroster. The system is vacuum-powered, and the default when there is no vacuum to run it is defroster.

Look for a small plastic tube coming through the firewall. It should be hooked to manifold vacuum.