I have been enjoying one of these for over a year so hope I can assist.
The majority of the heat heat is in the rear of the amplifier and this is the hottest section of heat sink. The front heat sink only ever get warm. The rear after three to four hours use get very warm at most. No problem with over 5 seconds with hand directly on top of heat sink. Mine is always run in class A, this is where the magic is.
A joy joy after class A 845 valves, very uncomfortable in summer. Just switch on an hour before use and off you go. Quality footers are also mandatory. Stillpoints or Wave Kinetics (which I currently use). Any more questions just ask.
Regards
Cyclopse