Need to replace the antenna on my 85 cutlass supreme. It's a power one. what kind of a job is this gonna be? Looks like I have to take off the fender.

 

You can get away with removing all the lower and side bolts and pulling the fender back and holding it back with a block of wood. However, pull it back just enough to get your arm up there. Pull back too much and the fender will deform, and not match the curves of the door.
Long sleeves are highly recommended.

 

Here's a link that may help:

http://tech.oldsgmail.com/echa_antenna.php

 

I wonder if you could just remove the plastic sheild inside the fender and drop the power anetnna that way?

I'm replacing with a fixed OEM antenna

 

If you have a plastic inner that is easily removable - go for it.
The mid-80s Cutlii had a unique inner fender arrangement that was part metal and part plastic. Also, tons of crap is bolted to the inners. It was easier on that to pull the fender back.

 

^^ Yeah I felt it real quick yesterday. I felt plastic and metal, but didn't see a seam

I did it quick cause it was raining like crazy yesterday