Basically that cylinder will be hot enough to melt/burn whatever comes in contact with it besides decent gasket paper (but there's a reason the head gasket is made of metal). There's a post somewhere that mentions the tip of the exhaust reaches about 1100 degrees (though I'm not sold on that being true), but yea touching the block for even a split second after it's been running a couple minutes should burn you quite severely. I tried to use a candy thermometer to measure it once, but it resulted in 8888 and kept turning itself on and off as if it was shorting itself out every time I touched the motor. I think it was something to do with the motor being grounded at certain intervals, as it did it even when cold. Maxed out a 280 degree meat thermometer after 1/4 mile trip.
Moral: Protect your wiring, and don't wear shorts.
A nicely tuned HT will run at ~180C when WOT up a hill.
That's ~350 Fahrenheit right? Yea, that seems about right.