A pair of these used to be fitted in my boat 220HP @ 3600 rpm, they were a bit sluggish in my boat and were upgraded to the same 4.2 L 6 cylinder VM engine but the 300 HP Cummins-Mercruiser version.
I am not aware of any issues with them but stand by for others input............
Certainly my new 300 hp versions are a pleasure to own.
When looking at them you will notice the coolant bottle is empty and should remain empty, it is for overflow only.
I have not needed any engine spares but service parts are readily available and you have a choice of
Mercruiser dealers
Cummins Dealers
Cummins-Mercruiser dealers
The last time I wanted an air filter I had the choice of three dealers at one Marina (Cobbs Quay poole), two could offer next day and one had in stock.