Most air cooled diesels that I can think of would be Deutz, Leyland made some but only in the UK from my understanding.
We have a Deutz at work that runs a blower for moving concrete powder. At idle it sounds like a sweet ol' 4 cylinder diesel. Rev it up and it sounds like it wants to take on 2 stroke Detroits in a noise competition...
We also have John Deere tractors at work, one 9330 and one 9560R. Now of course that's different than the tractors of old, but, I actually do like most everything about them. John Deere has an excellent parts network, you won't have much trouble finding parts, just lots of waiting and you will have to pay deerely for them... Caterpillar is worse though... but they can usually get parts to you faster.
Here at the farm we have two Case tractors, a 2012 Maxxum 115 2WD, and a 2014 Magnum 380 MFWD. The Maxxum is a comfortable, pre DEF, nice tractor, with strong hydraulics. But it is rather hard starting, and probably only makes 80 hp. It has always been this way, we bought it new in 2012.
That Magnum, I hate... it is too big for our farm, the transmission won't stay bolted to the engine, mostly thanks to Case's use of FRIGGIN ALUMINUM BOLTS, it drinks DEF like a pig, and is really quite uncomfortable. But it has power, and hardly drinks fuel. Seems poorly built.
I want to get an older loader tractor, like a 4020 or a 4320 JD.
Both at work and on the farm, we use 299D high flow compact track loaders. Have a 2012 here at the farm, and a dozen at work, 2019-2023, a few just got delivered a few days ago... but they get pretty unreliable past 2000 hrs, throwing emissions codes all the time, need to have twice as many loaders as we will use, so we have a few to run! Those newer ones at work are 299D3XE.