Is the experimental slant six with four rings an urban legend - or did I get the real story?

I was talking to a guy about a 63 pontiac I had bought with a transaxle. After I finished about the broken 1" tube torque drive shaft, the stupid design of a separate parking lever on the dash - and how easy it was to put the car into drive while in park - breaking the shaft ... then a quick recent story about a Dodge ... he returned with a Dodge slant six motor story. It is an excellent story and I had no reason to believe this guy would lie - but I did not really know him and I know how people will pass on urban legends as their own stories. Let me know if you have any information - legend, truth, or lie?

This was 25 - 30 years ago. I was trading car stories with this guy and started with the one above - about the pontiac transaxle. Then I told him about an incident a week earlier where i had purchased a 25.00 Dodge Dart slant six with a rod slapping around. I had taken it as a driver - planning to eventually walk from somewhere - steel was worthless back then.
I was on the highway, the knock got louder and louder, I was about 10 miles from home, and the piston shot out the side of the block. I watched it bouncing down the highway in my rearview.
I pulled over, the car was still running, and opened the hood. There was a piston head sized hole right in that exposed side of the slant six block - and it was shooting fire out of it.
I got back in the car and believe it or not - it made it the 10 miles home. I shut it off and it was locked up the next day. Tough motor.

Anyway - THE STORY: He says, "speaking of the slant six - have you ever heard of an experimental motor, a slant six, with four rings that was built extra heavy duty?
I said "N0" and he told me: I bought this 67 Dart with a slant six from my dad who had bought it used. His dad had told him the car had at least 200k miles on it according to the guy he bought it from.
His dad drove the car from 1974 to 1983. He never had a motor problem and put 300k miles on it - then gave it to his son (the guy telling me the story). So Rob gets the car and it has at least 500k on it. Brakes had been done a few times. Seven sets of tires. Etc. But nothing with the motor.
He drove it for 4 - 5 years putting another 125k on it. Now we are up to at least 625k miles. More brakes and tires.
The car has a hard time starting. It is popping and missing. He figures it is the timing belt. He figures he will pull the motor and rebuild it.
Then he finds a double timing chain. The head have more bolts than the manual says it should. He has bought a rebuild kit and not everything is right. His motor has 4 piston rings. He goes to a salvage yard and looks at another tore down slant six. His looks like it came our of a tank compared to the one in the yard.
He takes the kit back to the store and says he must have got the wrong one. The guy says there is only one for what he is talking about. He gives them a six digit number and the guy says it is too short. It ends with an EX.
The guy knows slant sixes and says I have no idea.
So he calls dealers, hemmings, etc. and finds out nothing. He looks at the ID plate and calls the plant it was made at.
He gets passed from person to person, until he gets on who is real interested and wants to know his address. He gives it hoping they are going to help him.
They come out with a wrecker and just take it from him. He cant get an answer from either driver - but they give him a check for 500.00.
He tells them he would rather keep the car. Neither chain is broke, just loose, and he can buy two factory chains and they will fit. It does not use any oil.
They tell him to keep the check. The car is "illegal" and should never have been on the road. " They gave us paper work to show it is stolen and told us, to tell you, we dont have to pay you anything - if you have a title it goes to another car. If you cause trouble you wont get the check. Take the check - because we Have to take the car.
They loosen up a little and tell him all they know. There were told to go get this car. It was never supposed to have left the factory but an employee who was allowed to use the car for a year in a practical demo never returned it - and had quit the job. There had been a lot of scuttle butt ever since he had called them and one old employee, before he was told to keep quite, said it was an experimental slant six they called the million mile motor. Extra heavy block, two oil rings, two timing chains, double geared, and a few other things I don't remember (something about the piston pins, heads, and valves - hardened gears). They had only made 6. Put one one on the road with an employee and a couple ran on stands for a few months. They were all eventually scrapped. The military application was the tow drivers guess. Only one motor made it into a car, the 67 Dart, out the door and into a possibly answered history.

Their guess was that it was an experimental engine - possibly for military applications and never intended for the general public - but that was their personal speculation.

My friend with the story thought it was an experimental motor designed by some engineer who had the pull to get it built. His guess is that a motor that would out last the car would make for unsafe cars on the road. His speculation.

My usual paranoid explanation is that they can always design motors like this - but don't because there is no profit making something that does not need replaced. Some high level engineer got the funds to build the design for this million mile motor - with the intention of scraping it.

I remember my grandad, born in 1887, showing me a light bulb he was still using and had used for 50 years. He said when I got it from a friend he threw it to me from across the warehouse where he worked (and they made light bulbs) and it bounced up to him. It had a rubber like coating with a filament that would never burn out. He never saw it on the market. I wish I knew what happened to that bulb. That was 55 years ago.

So - tell me, " the first time I heard that one...." or, more fulfilling, "yeah, we had some of those in the army"