It Looks a lot like the P7100 inline pump on my Cummins. What is it?

Yeah - I think that's the the early version , the A0100

Its an injection pump silly.

Some of the earlier tractors were dual fuel, started on gas then you switched it over to diesel!
So it could have had a magneto and spark plugs on th other side.

Duh! What kind?

The old late 30's to early 50s IH engines would open up a velve in the cylinder head to lower the compression ratio and start on gasoline. When you thought the engine was revved up enough, you would flip the lever you see on the side of the block to switch over to diesel. On gasoline the power sucked and in a tractor or dozer you had just enough to move slow on level ground.
The power unit you have photoed, looks to be the same engine used in a TD-20 crawler tractor or a smaller TD-15.

Great piece of History.

Steve

The small fuel tank in the photo is the Gasoline tank used for starting, the big tank was for the Diesel. What the power unit was connected to looks like an old mining compressor.
The mag is a six cylinder version of the A,B,H,&M farm tractor type will be mounted on a two bolt flange toward the front of the engine.
The intake manifold has two sections, the upper is for Diesel operation and the lower is for Gasoline starting. Notice the carburetor is very small for this size engine since it is only used for starting.

Do you know who owns this old Iron? I would say it is 1939 - 49 vintage.

Steve

brtzworld1 works for Navistar (formally IH) in the Melrose Park, IL engine testing facility. He may have access to more hard copy info.
I am a former IH Territory Service Manager for the Ag devision way back in 1980 and did not survive the down sizing.
As far as parts go, good luck brtzworld1 told me they don't even sell rebuild kits for the very popular DT-466 engine.
The best use for this old iron is some one who has an old IH crawler they need engine parts for.

Steve

I even have an IH M1 Garand Military rifle. Guess I am an old IH nut.

The small gasoline tank is visible mounted on the top right corner of the engine in the fourth photo down the page. The large one should have been used for diesel but some one could have put gas in it.

... let me know, I have done some antique tractor restoration and would never get rich doing it. So, if you need to know a few tricks, just act, there are several ways to do things right that work.

Steve