What's This Part and What Does It Do? (73 Cuda)

[68X426]

In the picture below, the arrow points to a part mounted on the firewall.  What is it, what's it do?

The car is a '73 Cuda, all stock.  The picture shown is with a 340 motor. 

A friend is looking to buy a '73 Cuda that has been modified to a non-stock big block 383.  This part is removed, with some sort of plate covering the hole in the firewall.  Any info is appreciated, thanks in advance.

[6bblgt]

heater blower motor

[ODZKing]

heater blower motor

Ya kinda need that if you want heat/AC

[4cruzin]

I agree!  Useful part of the car!   

[68X426]

Thanks guys.

[Alaskan_TA]

Take a look at the option list for 'heater delete' just for fun.

[68X426]

That's a good idea, he has the tag and BS, so I'll pass that on.  Thanks.

[ODZKing]

Heater Delete I believe is H25