I'm running a 24hp Honda on my little IH Cub Cadet loader tractor... I show it no mercy, and it hasn't overheated EVER...

We had Onan Performers on our Lincoln Ranger 8's, and our Miller Bobcats (welder generators) and the Lincolns would overheat, the Millers would not... but it was more because A) the units were INSIDE our 9ft enclosed service bodies, so airflow was limited  2) Some of the guys didn't have their exhaust sealed up too well, so it'd flood the interior of the compartment with exhaust and 3) the Ranger 8's had aluminum windings, but the Millers were copper... the aluminums were higher resistance, so they'd generate more waste heat than the Bobcats...

So this really isn't a good indicator...

I bought a small skid-steer (made by Hydra-Mac) that had the Onan NHCV (reverse cooling), and it overheated and burned up the machine (which is why I got it for $300), but that apparently was a common theme for NHCV-powered skidders, probably machine just as much at fault, as a skid-steer is a steel bucket into which dirt, leaves, twigs, gravel, stray tools, and all sorts of other debris accumulates, which rodents LOVE to make nests out of... inside the cooling shroud...

So that really isn't a great indicator either...

I have an Onan (prior to the 'Performer' moniker) on my mobile platform (it started out life as a detassling machine).  It NEVER overheats, but that's because it doesn't run well enough to work hard enough to get hot...

So that's not a fair indicator either...

I had an Onan MCCK 5 generating plant that ran at 1800rpm, like a watch, started perfectly, every day, without a choke, and never missed a beat, but  every so often would make a really loud WHACK, like there was something in the shroud, that got picked up by the flywheel, and I had it apart a half-dozen times and simply could NOT find any reason for it...

So that's not a fair indicator either.

I CAN tell you, that if you call Cummins-Onan for ANY parts, or ANY support, or ANY advice... or even the time-of-day, they are unlikely to have it, wouldn't give you an estimated time of availability, or even quote you a price... but if you order it, you'll wait for it, AND... have either a stroke, aneurism, or myocardial infarction when they hand you the bill...

So if you're building a working machine... consider every possible option, and even a few impossible options...