Can anyone tell me if a twenty-two year old Savage .223 with a 26" heavy barrel is large shank or small shank? The barrel measures about .800" at the muzzle.

No doubt it's a small shank.

There is a difference that you can easily measure between large and small shank. the barrel nut of a small shank is 7/8
" and a large shank is 5/8",

It'll be a small shank.

I called Savage and talked to a lady. She didn't have any idea. I told her I would like to speak to technical. She said, "I am technical."

I came up with the idea to call Pac-Nor since I bought a few barrels from them. The lady who answered the phone said, "Oh I know that one off the top of my head. The small shank is 1.05" and the large one is 1.117". I've been doing this for ten years and it's old hat." So the one I have has a small shank. Now I can order the correct barrel.

I'm pretty sure (based on age) your action is set up for a small shank barrel.

I've got no idea how you're correlating muzzle diameter to shank size though.

You didn't notice the question mark after the shank question. The muzzle diameter was general information for those who might be interested.

Gotcha, Pacnor makes a great Pre-fit for Savage,

Good Luck with the project.