Thanks Dave. I have a fair amount of experience with 'hot rodding' starting with stuffing a 440 into a 65 Dodge Dart 30-40 years ago. I'm capable of modifications and knowing when I need to have someone else do the modification. My primary issue/surprise here is when someone sells you something that is advertised to be an exact fit (ie it specifies is fits my application) it is not. This is a learning as I move through this restoration process. Thus far the radiator has been only one of several issues I've faced in just getting the car started including very simple things like finding appropriate hose clamps for my fuel lines. I'm learning nothing is easy or cheap as I want things to 'look nice' and work. Fortunately there is help and a lot of people who of gone before me (such as yourself and others) that will make it less painful. Note that I did not say painless.
The price of an exact fit from Griffin makes me think I can modify things and get this one to work fine. Had I known this before I spent money on this radiator I may have sprung for the extra bucks. But I'm stuck because if I were to sell the one I have what would I call it? "For sale, a radiator that sort of fits a 63 Impala." They'd be busting down the door.
While I'm thinking about next steps and I know this breaks forum protocol, I am now assuming that people who make sheet metal replacement pieces don't all have the same quality of product. Before I buy floor pan pieces I may need some help in understanding who makes the better exact fit sheet metal. The car is pretty solid less the floor pan area right under the front edge of the front seat on both sides. I'll start another thread if I don't find what I'm looking for via a forum search.