Just to be clear, the video I submitted was something I found on Youtube; nothing to do with me whatsoever (unless drooling counts as something to do with me)

FWIW when I fixed my Lister VA I replaced the original aluminum piston with a cast iron one and it didn't seem too badly off-balance; it just skated rather gently across the floor.
I realize this is opposite to what you are proposing to do, and it is certainly not running at 850 RPM but hey, nothing ventured nothing gained. There is a lot of info on this forum about engine balancing.

I was unable to free the stuck rings on the original piston, which is why I replaced it.

I have not run the engine very often, but I do have a new aluminum piston for it, when I get a chance to change it.

https://www.youtube.com/watch?v=kYbySo-28pI

As you can see in the video, my son is standing on the wooden skid to help slow it's movement across the floor.

I am still looking for an original fan shroud for it, in case anyone has a lead on one.

Hi Bob, I recently fixed an ST2 which had a stuck injector nozzle; maybe you could give that a check.

I remove the bolts securing the bearing plate behind the flywheel. Flywheel, Bellhousing, Governor weight mechanism, Piston, rod and cylinder removed  of course.
Set the crankcase with crankshaft up in the press, supported outside the OD of the bearing plate. The crankcase will need to be elevated approximately 3" to allow the crankshaft and bearing plate to move downward.
Press the end of the Crankshaft only... Not the gear. I use a socket that is a bit smaller than the end of the crankshaft inside the gear, to press against.
The Crankshaft and bearing plate will come out the back of the crankcase, leaving the gear behind.
I use a 12 ton press for removal and installation of the gear.

Here is a PH2A that I did a job on some years ago.

https://www.youtube.com/watch?v=9lmmtqb74B4

Congrats, and yes, a video would be great.

Hi StrawHat, I think this is one of the tractors you are referring to.
https://www.youtube.com/watch?v=Rxdka2igpRk

I share your interest in old semi-diesels. I also have considered converting an existing engine to semi-diesel just for fun (maybe a Listeroid or hit and miss gas engine?).

I recently considered it with my 1920's Nelson Bros. gas engine (4.5" bore, 6" stroke, dual flywheels) which needed an entire top end; and I even went so far as to purchase a suitable sleeve and material to fabricate a cylinder with.
But the local historical value of the engine was such that I could not bring myself to do it, and sure enough I have obtained a used cylinder, head, piston, and rod for it.
So a restoration of sorts will be started on that one, depending on what the future holds.

With the Listeroid, I can't find a reason to justify the expenditure it would require (and do I really want to ruin a brand-new engine which I could possibly sell?).
Even if I did convert a Listeroid to semi-diesel, what would I have? Half of the people I showed it to would not understand what I was talking about when I explained what I did, and the other half who did understand, would probably condemn me for doing it .