Hi again. I found it! The songbook is called "Golden Guitar Pop Instructor / Volume IV: CLASSICAL GAS", and features a hand-written (by Mason Williams) arrangement of that song. A Charles Hanson Publication, from sometime in the 70's. "Napoleon" is on page 66, and listed as "Copyright 1961 by California Music Press". It's is 2/4 with 4 sharps. Pretty much as people have reported:

I had a horse his name Napoleon
All on account of his boney parts.
He was bred in old Kentucky
I'd holler "race" and off he'd start.

He was so thin you could see through him,
Hair all over as fine as sink,
Drove him to my milk wagon,
When I wanted him to stop I'd holler "Milk"

One day while driving through the city
'Long came a "Jay" with a rig so neat
He said "Come on Reuben,
We'll have a race right down the street".

Away we went helter skelter,
I was ahead and I laughed in his face
Sure as a sinner, I was a winner,
Till he holler'd "Milk" and I lost the race.

All the best,
Jack (Kitchener, ON)