I kept seeing all these great radiator reservoirs at the yard, so I bought one for about a dollar. I was thinking adding one and routing hose would be big benefit to keeping coolant in it, as well as easy way to check coolant level.

If this one doesn't mount/look right, there are about 500 other styles to choose from out there. Most are fender mounted, so something will look ok under the hood.

On the flipside, I'm no engine genius, so I figured if this was such a great idea, why don't I see more people doing it?

Any thoughts on if it works? Do I need a different style cap? Other things to think about? I'm trying to stay somewhat original, but if it keeps it from running hot one day, I don't mind giving up that particular piece of originality.

It works very well. You will need a different cap with a gasket on the top of the cap to seal it to the radiator neck. Get a cap for a closed coolant system. If you want the car to look original like for a car show, make the tank easily removable (mine is mounted with one bolt) & take it out when you go to the show.

BL