Jack,
So far, I haven't heard from anyone who thinks we actually need .060" clearance to intake valve, and your dropped valves can hardly be blamed on lack of clearance in my opinion. The main reason I ask the question, besides all the advice that "you need .060" clearance", is that I could increase my compression ratio by going to less clearance. Maybe only half a point, maybe more turbulence and better combustion, but as you know, every point counts.
I only have one race bike here in Nova Scotia to play with - - 1968 Bridgestone 350. In case you don't already know, that's a twin cylinder, rotary valve two stroke, 6 speed transmission, dry clutch. So far, 114.xx mph at Loring. So again, no valves except the rotary ones, but no spares available, so playing with a bomb.
Tom