I dont know of anyone making a diesel I-6 that small unless its GMC. It would have a lot of torque but only on the lower end and its rpm range would be severely limited to around 2500 RPm, due to the stroke of the crank.
GMC did make a 53 series (53 cubes per inch) inline 6 at one time, but only saw one or two of them, the reason being was that the predominate 53 series 6 was a V configuration and we had them in the PBR's over in Nam, and are in use in a lot of diesel powered cruiser boats. They were rated at 160 hp, and peak rpm was about 3500, but you didnt want to keep it there for long.
3500 rpm was what I meant with the 300 inline as well, not 2500.
The general operating range was from 500 up to 2800 rpm.
Oldsmobile had a 350 cubic inch diesel that was loosly based on the Olds 350 gasoline engine, and it was somewhat gutless. A lot of guys got ahold of the Diesel and converted it over to gasoline. I think all it required was using the heads, intake, cam etc from the gasoline version.
There was Ford I6 diesel used in the mid 80s in the Lincoln Mark IV. It was actually a BMW slant 6 used only for 1 or 2 years. They were difficult to work on, leaked oil and diesel fuel, and needed a ton of special tools.
We only had 1 sold at our dealership and had only 1 other come into the shop for service.
I have seen a strait 6 ford that looked just like a gas one,but it had the injectors where the plugs would be,it was on a big generator. About the olds,I think it was likely a 350,they look like a 455. They were sort of neat in the respect that the later year ones had a stronger block, 3 compression ring forged flat tops,real beefy rods,455 size mains and a roller cam,they could be changed to gas by putting the gas heads and a intake on them and regrinding the cam. The gas heads don't flow that well though, but they made for a bulletproof truck motor,great for a diesel retrofit.
I have a friend who is thinking about keeping diesel heads on one,but putting a gas intake with a distributer on,setting the heads up for plugs and running alcohol at 20 to 1 compression,not as a go fast,but for economy.
Ak Miller built many big Ford sixes and was running one for a while that used a mechanical Bosch injection off an older Mercedes (it was current at the time), that has the appearance of a Diesel pump. There were many pics circulated over the years of this engine and most shots showed the injection pump ( usually why they were taken) prominently while the dist/plug wires weren't as visible. Someone may have seen these pics and assumed it was a diesel because of the large mechanical pump mounted on the side of the engine.
I remember Akton Miller quite well, so you know that puts me in the dinosaur bracket. I used a template of his for installing motorcycle carbs on a 250 cubic inch Ford 6, way back when. That was a torid running 6, but we never were quite able to get the slight hesitation out of it at 1500 RPM. We put 6 32 MM mikunis on it. Lots of guys swore up and down it was a Jag or Farari engine even with the stock Powered by Ford Rocker Cover.
That Bosch system mentioned by woodz428 was a common setup back in the 60's and early 70's for running fuel injection on dirt track cars.
Unless it was a converted over gasoline I-6, it would most likely have been a Catipiller, Detroit Diesel, Volvo, Cummins or International Diesel, since Ford doesnt have a proprietary diesel and those are the two that make the bulk of Fords diesels for them. Or I should say they havent had one up to the last couple years that I know of.
I do know that Ford bought out Volvo a few years back so it could be one of their diesels with a Ford Rocker cover on it.
Well, that could be I guess,I don't really know what they look like that well,but before I saw anything that even said ford,I thought it was an old 223 gas motor from a far,then I noticed the injector pump as I got closer and got curious,I don't know.
Ford has an I6 diesel in the 60's used in smaller trucks, C500 and so forth. It was about 280 ci. It was made by Ford of England, at the Dangenheim plant, and was derived from a tractor motor. They were rated at 110 HP. I have seen one in a Ford pickup, not a factory install, they don't fit well, a bit too long. Hard to find parts for even then.
A Perkins out of a Massey Ferguson Combine would be a better fit, and some of them had turbos on them.