what other a/c will fit???

[CJJ67]

Just curious if this is possible. Besides buying the aftermarket a/c units like vintage air, what a/c unit can I use from another vehicle that would be hidden under the dash? Is there a car or truck that has an a/c unit that I can use or customize to fit my 67 chevy stepside? Also can you buy the firewall attachments for the a/c and heater hoses seperate? Again, just curious because I can't find anything other than aftermarket info. Thanks...