First of all, I've mentioned two alternators: a Delco 28Si I'm using on the trawler and an Electrodyne I'm using on the sailboat. Delco says of the 28si: "125 dec C temperature rating". (I said 120 above but reviewing it again it is 125). They do not elucidate beyond that, but it cannot mean 125 dec C ambient, or if it does it comes no where near that. Based on case measurements, 125 deg C measured somewhere on the alternator is pausible. It is an ordinary medium framed J180 mount.
The Electrodyne on the sailboat is an entirely different animal. It is MUCH larger than the Delco and an entirely different design. There are no brushes, no slip rings, and no coils of any kind on the rotor. Their literature suggests routine maintenance of repacking the bearings every 20,000 hours operation. Up to about 1400 rpm it is a net current sink, break even there, and then rapidly building to full output. The rectifier pack is external to the frame but mounted on it. It is being controlled by a Balmar 624 and I've never seen it cut back due to temp (but have taken no temp measurements). The temp sensor is on the rectifier pack. I've seen it produce 300 A for awhile, but my battery (440 AH @ 24V Lifeline AGM) cannot absorb that for very long. I seems to be able to do 250 - 280 A continuously, this happens sometimes charging the battery while running the watermaker and freezing the refer plates simultaneously.
Here is the installation. This is the original driveshaft I built, with a Spicer coupling on one end. That proved to be problematic and failed one day (actually it loosened on the alternator shaft and there was no way to tighten it) so I replaced that with another rubber coupling. That absorbs any misalignment and also the torsional vibration from the 4 cylinder (Volvo D2-75).
Here is the modified driveshaft, rubber at both ends (Vetus BulFlex prop shaft couplings). These have clamp type shaft couplings eliminating any play:
Installed. The SS ring around the shaft is intended to act as sort of a NASCAR drive shaft catcher - if the alternator end fails and comes loose, I didn't want it beating a hole in the hull before I could get it shut down.
Here is the whole installation. Notice the size of the alternator compared to the 2L 75HP engine: