I finally got the tach installed and not too soon. Gained a good finger of knowledge, too. I clocked 7600 rpm at 33 mph uphill, no lugging, WOT, and a little four-stroking on top. No undue vibrations; they must have got lucky with the balancing.
(...uphill, uphill, uphill)
Yes, uphill, which means the engine got HOT, around 350F. As soon as I pulled the clutch, she ran away! I killed the fuel, tried to cover the carb (didn't occur to me to choke it). She was starting to smoke, very scary! It only stopped when I accidentally popped the clutch lol.