Not sure about 67 cars, but on the 61 Galaxie there is a bracket on the inside of the door that acts as a window stop. It prevents the window from going to far into the door when you roll down your window. I replaced the window felt on my 61 and the only way was to remove the windows. 

I have a 67 convertible that i replaced the weatherstrips on it and you can lower the window by removing the lower stop bracket in the bottom of the door attached to the window. But you will not be able to remove the fizzy's with out removing the vent window assembly in order to remove the screws behind it.

Yes and No, it all depends on your mechanical ability. That being said, it can be a frustrating job or easy, it means taking your tome and noting where ever thing  goes when disassembling. It would help to have a shop manual as to assist you. My way is to let the window stay in the bottom of the door as you remove the vent frame. That way you can get at the weatherstrip for removing and then replacing. After that you will wish you had another hand on your body to help. All mechanics should be born with three hands and arms to make there lives easier, ha ha ha.Hope this helps.