Replacement Heater or AC unit after smoothing firewall??

[Wildcard]

Hello I am thinkin of smoothin the firewall on my Non AC 67 chevy and would like to know a good replacement heater slash AC assembly that can be install possible something some one has remove from a smaller car or truck that works well or something like that. Would like to install a Vintage air Unit but they seem pretty spendy.

What would you all recommend or have seem installed before if any??

Thanks, Wildcard