AC Evaporators, Condenser and HeaterCore Manufacture needs help from the ones doing the installs

I'm 74. So I'm not as "agid" as I used to be. I have a few, disorganized. Ping me with a "conversation" (used to be PM) every month or two to remind me. I think I have a near complete AC box out of a 69, and a later 73? 74? have to figure out. I also have an earlier heater only box, 67/ 68 or so.

Are you able to find some old 3rd party catalogs with illustrations such as Everhot? And I no longer remember the other brands

You say you downloaded manuals, did you get both service and parts manuals?