Your heater blower motor will still be fine when using a knee knocker with it's own blower motor. It was when using the factory integrated system that the heater-only blower motor was not adequate enough - hence the larger motor. With the knee knocker you don't need to change the rotating rod assembly (I would change to the V8 cable style) nor change anything to do with the bulkhead connector opening. I am adding OEM factory AC to my wagon and ended up changing the firewall to an AC firewall to accomodate the changes that are required. Take a look at my wagon thread for when I was working on the firewall and you can see the differences in the non-AC and AC firewalls.
I should also mention that the limited real estate in the early A engine compartment necessitated a drier that was mounted horizontally on top of the passenger inner fender. The more common vertical driers tended to share real estate with the alternator and horns. That all changed with the wider 67 so more traditional components could be used.
