Classic Auto Air AC- things to look for

Thanks a lot for the details. I have a unit--not sure where it came from--but the under-dash unit is VERY small, much smaller than the original heater only. I don't have it installed yet, but it's obvious that "modifications" will have to be made. The heater hoses don't exit through the firewall, EG. You have to provide your own routing Neither do the AC hoses/ tubes