I would agree 100% with what Pat has said and will add a few other comments---

First with a close to stock cam for a street driven car, none of this will result in much change--you will need to get upwards upper .600-800 lift cam before you need to start to do this---First off you have to check for camshaft/connecting rod clearance for several degrees advance/retard from straight up timing( so you will know the limits of advancing /retarding cam) And to do this on an assembled engine in a car pretty much gets you to the point that a Jessel belt drive with the long water pump is needed--also any cam advancining/retard necesstates an reset of the ignition timing(unless crank trigger)
Heads, springs,valves,lash caps, guide plates/slots/rocker alignment--all need to be set up for the lift of the cam plus checking for valve /piston clearance at advance/retard limits
Changing valve lash is pretty much limited to a thou or 2 because of limits of cam lash ramps and types of cylinder head/block materials(alum-iron)
Rocker ratios should be utilised that are highest ratios possible