Update: i have two sets of factory adjustable 273 rocker arms/shafts both reconditioned with bushing inserts. One set is "virgin" so to speak (no signs of grinding for spring interference problems). The other set shows signs of some (not all) rockers having been ground down slightly to improve valve spring/retainer clearance problems by a previous owner.
When the virgin rocker set was installed, one rocker was definitely touching a valve spring. When the "modified/butchered"" set was installed, I was able to experiment by switching rocker arm locations on the shaft here and there until none of the rocker arms made contact with the springs. Of course, clearance is pretty tight all over, some with less clearance than others. And the funny thing is that some of the rockers with the most clearance have no evidence of grinding mods. It seems the original casting of the rockers was not an exact science.
So I called Mike at B3 Racing Engines who coincidentally has been following this thread. I asked if rocker shaft shims would help alleviate the small clearance between the new stock 340 valve springs and rocker arms? He advised against that, citing that may very well upset geometry. He suggested looking for springs with a smaller outside diameter.
To get an idea of the current geometry, I placed a little dab of Lubriplate white grease on the valve stem tips and tapped the valve with the rocker arms. Of course, this is just with the valve closed. The pattern looks to be this: the rocker arm tip contacts the valve just a hair back from the center of the rocker arm tip. On the valve, the contact point looks to be just a hair toward the engine centerline, but pretty close to the center of the tip. (valve lift apparently will be .441/.472). I don't see any big problem with geometry at the moment.
View attachment 1716312798
View attachment 1716312799
View attachment 1716312800