Flip,
I don't know how or why you choose the spin off on emissions.
Common rail fuel injection doesn't really have anything to do with emissions, it has to do with a more accurate fuel distribution and performance system.
You can get about 20 better economy and performance out of a common rail engine.
Your mechanical fuel sucking M's would do much better with a common rail system giving them fuel properly when they needed it.
Because emissions hardware make an engine more complex and less reliable. The reliability downgrade comes at the expense of lowest bidder components and don't tell me Kubota manufacturers their own emissions components because they don't. You know that and so do I.
Far as my M's sucking fuel, I find them to be pretty efficient and much simpler than current engines. Never had a concern about fuel used per acre run. I find them both to be very efficient, one reason why I bought them in the first place. Now my old Case with the inline, turbocharged 6 was a guzzler.
But then I'm not dumping raw fuel into a DPF cannister to burn particulates nor do I have to worry about the end of life replacement of that cannister either, 'cause I don't have one. While on that subject, no EGR valve to coke up either. No need to park the tractor to let it regenerate or worry about warmup idling. Bet I'd really plug the DPF when I warm up the 9 for 45 minutes when it's real cold outside so the hydraulic oil is flowing properly.
The schematic of the CR injection system with all the components is far more complex than mine with a lift pump, filter(s), injection pump and injectors. Like said, complexity breeds failure especially with lowest bidder components.
If I live long enough I may be stuck with a Tier 4 final engine, but I certainly hope not.
Why I have my eye on a used Deere 90 horse FWA utility tractor that is pre-Tier 4.
The way it's going, I suspect lawnmowers will soon have catalytic converters too.
The current crop of Tier 4 final diesels reminds me of the cars of the 60's. Festooned with emissions crap that was failure prone and did nothing for life expectancy of the engine.
I'll just stay moot about emissions hardware because I don't have (nor want) any if I can avoid it.
Hopefully, the builders will get it sorted out like the automakers did.
Until then I just chuckle when I see the guy down the road with his big Deere track machine sitting in a half tilled field with the service truck next to it with the technician trying to diagnose the issue because the engine derated and the tractor is for all intents and purposes a rock and the farmer has a schedule to keep that he's not going to. Might as well retire to the barn and get loaded while the dealer try's to figure out what happened and then fix it, if the parts are available that is.
In 2200 hours on the 9 and 1900 on the 105, I have not experienced one engine failure related to injection or anything else for that matter. One failed lift cylinder on the 105 that was under warranty and that's it.
...and they both get worked and worked hard because I have schedules to keep too. Neither are hobby tractors.