A/C --> Slant 6 --> 440?

And don't forget that you have to mod the blower motor/box to fit the 440, with or without AC.
A couple good options in the How To section- just remember your AC box may vary a bit, these articles focus on the standard heater box.
Heater Box Motor Modification for Valve Cover Clearance | For A Bodies Only Mopar Forum
Heater Fan Motor Mod for Added Engine Bay Clearance | For A Bodies Only Mopar Forum
Another blower motor mod for BB. | For A Bodies Only Mopar Forum