Heat versus AC/heat box interchange

are the mounting studs in the two boxes even remotely the same? I don't think so... I have been running an A/C box with all the A/C stuff removed from the box and an A/C heater core in place in one of my cars for many years with no problems. The vacuum switches in the dash actuate heat and defrost, but there is no dehumidifier in the system for defrost like in an A/C car