Welcome, My '68 was originally A/C equipped but as a child, I pulled everything off from the firewall-foward. I had a cover made for the firewall and used the same heater core. The HVAC box is in tact but aged. With that in mind, my modes all switch as they should and defrosting is not a problem. I must assume you are missing some or most of your HVAC box? The blower comes on, but wont direct to defrost? When you move the lever to defrost, are you feeling any resistance? You may need to remove a few things so you can see what is / isn't happening when you try. I'll bet someone reads this and posts a parts illustration or something that will put it in proper perspective for you. And again, Welcome to our (mostly) happy family.
