72 Slant Six running too cold

When you put your hand on the rad after driving it does it feel hot or just warm? If you can't lay your hand on it got to be in your heater box some where. Since you had it out I know there is no debreis clogging the core. (had that problem before) That heater should melt your foot off. I know it will be a pain in the back, but, with the car hot disconect your vacuum motors and manually move the airbox doors. If you get the desired effect you found your problem. If not....