It should be a fairly simple job that you can accomplish yourself, although it can be a bit fiddly and you need to be a contortionist to some degree to actually get access to the parts.
I am going to assume that the setup for your rag joint is very similar if not identical to C bodies, although I don't know for sure about Imperial until I look it up which I can't do until I get home from work... but in 65 C bodies the rag joint heat shield is held on with a giant Corbin clamp - if you don't have the right tool, removing it is a pain i* t** a** and potentially dangerous. However, I hear you about the little sheet metal screws that they moved to in 66 being being such a drag to work with! See if you can go to your local auto parts store and rent borrow or buy a Corbin clamp or Spring clamp locking plier set. It makes the job of removing Corbin clamps easy and safe. One of the best tools I ever bought.
Do not dispense with the heat shield, as difficult as it is to deal with, as it's there for reason.
Once the heat shield is removed you have access to both sides of the rag joint. You do not need to remove the steering column or take anything off the car - all you need to do is undo and remove the fasteners. They are (if memory serves) 3/8 or 7/16 lock nuts with lock washers and cotter pins, and the bolts heads use a quarter inch or 5/16th hex key.
There should be 2 of them. Spray them down with penetrant before you attempt to take them off.
There is either a coil spring with loop ends, or a wire with loop ends running down the center of the rag joint,connecting to the fasteners on either side of the joint. This is the grounding connection for your horn, and if you don't replace it then your horn will not work. If it's in any way suspect just make a new piece of wire about 3" long with 2 loops on the end that can go over over the bolts.
PM me if you've any questions.
EDIT: The parts manual shows a different part number, so I don't know what the difference is between the C body one and the Imperial one. I will try to have a look in my 65 service manual tomorrow, but in the 66 manual, the parts shown look the same.