I tried lashing the valves on my Valiant while it was at idle. I never was able to get a feel for the correct amount of drag on the gauge, so I just used the EOIC method. I installed crank bolts on my slants that didn't have one so I can use a ratchet wrench to turn the motor over the 4 times required to set all the valves.
For the first time 'lasher', it's best to set the valves at .012/.022, better a little loose that too tight. Once you get a feel for the gauge, go with .010/.012.