There does not seem to a definitive answer to the question, tho.
More recently than 2008, and I do not recall the year, a mechanic friend of mine brought over his answer to the potential problem of air pockets. It was a 12 volt pump with a five gallon bucket, and a handful of small hoses and pipe pieces and clamps.
Basically, he opened up the hose connection from the engine to the hot water heater and put the hose from the new 50/50 mixture into it, pushed by the pump. Another hose link ran into an empty bucket to catch the old coolant. In a short time the new coolant was pumped in and the old was pushed out. With some minor spillage the engine hose connections were re-established.
I did not use this scheme last year for our new Beta (also a Kubota block) and just poured in the coolant at the "high point" at the top of the heat exchanger. We have not seen evidence of any air locks. There are probably internal differences in all of these blocks, even tho the external parts are so similar.
I recall that when I opened the petcocks on the lower part of the old M25XP to drain out the coolant before we lifted it out, it seemed like less came out than the manual indicated for its capacity. I ended up capping all of the hose ends to reduce the mess when we lifted and tilted it, going up and out thru the hatch.
Had to changed coolant recently in my m25xp. Ended up with a nasty airlock. Nothing worked. In the end I took the petcock out and filled thermostat housing with coolant using a syringe and that did the trick. For the next time I will be replacing that POS peacock with a normal ball valve.