Back in the day it was important to ensure that when adjusting tappets the ones being adjusted were on the back of the cam especially if it had quitening ramps. This was typically achieved using the rule of nine for four cylinder eight valve engines or as above, finding TDC firing stroke and being able to adjust exhaust and inlet together.
To ensure both inlet valves on each cylinder are closed for the purpose of cleaning though surely a visual inspection of inlet valves closing completely plus a further quarter or half turn of engine is enough.
