This is a job for ---superwrench!
Eevn YS screwed this up so badly I could not believe it - a few years back -and they never admitted it.
the travel of the valve - must always be less than the effective closed length of the valve spring.and or keeper /guide
On the original 120, they designed in .030 over travel -so there was plenty of clearance.
then-- they reground the cam lobes to increase the valve lift --aprox--- .030.
I got one of the first of these high performance regrinds .
RickMattie was working at YS/Futaba then.
I called him -he said "no way "
I said - "check it out" -
I fixed my engines -which had the spring keepers bottoming on the valve guides - with a little Dremel work .
PS they were having problems with the cams and lifters -
surprise surprise.