I think I understand the purpose of the Evaporator Tank on top of my fuel tank, I assume it is a charcoal canister. Any idea if it can be modified? I would think a remote charcoal canister would accomplish the same task, and allow me to utilize some of that space. Any thoughts?

There is an evaporator/expansion tank AND a charcoal canister. Pre-74 the charcoal was located on the tank. Later models had it in the engine bay. All years have the expansion tank.

So you can relocate the charcoal canister, the factory did.

Why do you want to modify the expansion tank? What is your goal? (I've been there and done that, just curious what you're thinking.)

I am putting an aftermarket ac evaporator in my cowl and am notching the gas tank to make it fit. I have relocated the wiper mechanism to a 996 unit, now I am modifying the tank.

And your goal is what?

My goal is to have an ac evaporator which fits in the space. Modifying the fuel tank and expansion will be needed.