There is not Bentley manual advice on "specs on valve
clearance (adjusting valves and measuring gap w/ feeler
gauge, e.g)" because these engines have hydraulic valve
lifters.  There is only initial adjustment, the
purpose/benefit of hydraulic lifters being that periodic
adjustment is not required.  This subject is covered very
completely at

http://www.bostonengine.com/articles/hydraulicll.html