So, here I am updating what I have found out so far. Tractor has 2,908 hours. Trans, etc are fine and don't leak.
1) 1 bad injector
2) 1 bad glow plug
3) broken compression ring on #2 and bad overall condition of the piston and other rings
4) cracked cylinder head on #2 between the intake and exhaust valves
5) All intake valves damaged beyond use. Pounded to the point where they have a neck and sharp edge.
6) springs seem weak as I am easily able to push on the springs and open them about 1/4 inch with my unassisted hands. Retainers look fine.
Searching for parts took a looooong time. Most places did not have what I needed and the prices ($1,200 for a set of rings. Insane pricing. No typo there. I contacted 2 different dealerships), etc.
I did my research and found out that this engine was designed and licensed to Kukje by Cummins. So, there is one major design change in 2004 (mine's a 2011) where the engine went from sleeved to bored in block. The later engines are said to be more durable and run cooler. Many skid steers and other construction equipment use this Cummins engine.
I decided to contact one of the Chinese companies advertising on Ebay. They were incredibly responsive measuring the pistons, etc. I purchased the rebuild kit including pistons, rings, bearings, gaskets, for $500 or about 1/5 the price from Branson, and that is IF you could get parts timely. They company in China also told me they would throw in a set of intake/exhaust valves, guides and seals for no cost.
The shipment was partly delayed due to the communist lockdown of the country, but arrived last week. I was out of town and when I opened the package the parts are excellent! Well packaged and have a brand that says "Mustang" on them.
In examining the parts I find them precise. Identical. I also found out the head gasket has a few orifices that the orig gasket did not and in examining the head find that the orig head gasket SHOULD have had holes there for water flow. So, perhaps Branson engine builders did not use the correct gaskets originally?
The block needed honing and the ridge removed, but looks good spec wise. The rod bearings do have wear and you can see the copper coming through. The crankshaft is excellent. The rocker shaft and rocker arms and push rods are within specs as well.
It seems clear that the engine overheated. My guess is poor maintenance and lots of starting fluid. Even the combustion chamber on #2 looks pitted and partly melted.
There was no issue with oil pressure, so though I will pull a main bearing, I believe they are going to be OK. I may replace #s 2,3,4. But replacing #1,5 require much more work as you need to remove the lower block skirt.
Since repairing cast iron properly is a LOT of work to do correctly, I am just buying a dressed head. From China as well. I will post photos later today or tomorrow.
