Yes, that .140 is far more than enough to eliminate in-operation clashing. Your analysis makes sense, pretty much eliminates the chain drive variable and given, say, tight .002 or so guides and a revised valve pocket location that problem should go away.
On those guides, I wonder out loud if the cammer's unique rocker arm, cams that push the rockers differently from one head's side to another, et al, have an effect on guide wear as opposed to mere lack of oiling (my comment on PC seals earlier). Can't imagine though that the SOHC rocker arms, even with your high lift/duration cams, could cause that unwanted swiping action that can push a valve sideways more than up-down, the same effect as a too short/long pushrod in a non-OHC engine. Does this engine's sweep produce a narrow valve tip mark like a pushrod 427 or is it substantially wider? Remember the worn, non-hardened tips you showed on some cammer valves awhile ago but didn't catch the sweep dimension.
I also forget if these are B. Coon's heads or what. Not to knock them but if the guide material isn't wholly compatible with your SS valves, guide wear can be accelerated as you know. 'Course, if the valve's head perimeter was grazing the piston pocket at speed, that alone could cause rapid guide wear!
I wonder too if the engine has a few valves that did not touch the piston's valve pocket (if not all of them did) exhibit normal valve guide clearances (whatever you set them at initially)?