I have recently replaced my firewall in my 71 cuda. Been thinking about smoothing the firewall up and maybe filling the holes for the blower motor and possibly the heater hoses. But I want to have a heater for the defrost function. Has anybody used a universal heater box and plugged the factory holes in the firewall?

I use a heater from Summit in my '66 Charger. Some day I'll get around to restoring the factory heat-a/c but for now the aftermarket system works fine.

I have one for my car, haven't installed it yet though. It's a universal heat/ac system. I smoothed my firewall and welded shut all holes. I will need to drill some holes to run the heater and a/c hoses through, but the system is flexible enough that I can place the holes wherever I want.

System consists of a heater box designed for under-dash application, however it also has cutouts on the sides to attach duct for remote air distribution, like defrost which IMO is a necessity.

How does it attach to the cowl for fresh air? Or does it just recirculate? Are you able to use the stock defrost ducts?

By default it is recirc only. However it has provisions to attach dual 3" hoses to the blower motor inlets. those could be piped up to the cowl if you made your own adapter plates.

To get air up to the windshield I will have to rig something up to attach the after market air box outlets (2-3" round) to the stock ducts. I was thinking of making a duct adapter out of some scrap aluminum or steel cutoffs. Not drag and drop but cheap and effective. You can also buy y-splitters with control cables if you want to direct inlet or outlet flow.

Thank ya sir. It sounds doable just have to make a few parts.

My '47 Power Wagon has a similar vintage Ford heater. I don't know the story that put it there. Does that count?

More seriously, effective defrost needs either fresh air intake or refrigeration (AC)... sounds like you are going the fresh air route. Most aftermarket systems do not have fresh air.

On the Power Wagon, fresh air comes from generous air leaks...

Mine looks similar to this in the back, with the blower motor in the middle and the two bird cages on the outsides. As you can see, the air intake duct faces outwards allowing the installer to add two fresh air intake tubes. Outlets on the box are similar, round.



Similar to this, however mine has the under dash style vents facing forward and the round outlets facing sideways.