I recently installed 1.6 rockers in my 305. The car is nothing special so I just bought some Crane stamped ones. The head has the pushrod guideslots in the head. During the install I noticed that the pushrods were close (really freakin' close) to the bottom of the slots. I thought I would get away with it and almost did. I had been warned that this can happen on 1.6 rockers, especially if the head had ever been cut (mine had).
The symptom was that the car made a lifter noise on start up, this was very minor, but nevertheless it was there. Not one, but several, and intermittantly. Once the engine was raised just above idle the noise went away. I suspect that the pushrods rubbing on the guideslots, caused the lifter to collapse at idle, when the rpms were was raised, the increase in oil pressure forced the pushrod to move and the noise went away.
The fix was to remove the intake and pushrods/rockers. Upon inspection you could see where the pushrods had rubbed against the slots, nothing devastating but enough to cause problems.
At this point I taped up all of the ports in the head, cleaned up all of the oil in the lifter galley, coverred everything in rags and masking tape. I used a die grinder with a 1/4 inch bit and carefully (really really really freakin carefully) opened up the bottom of the guideslots. I used a pushrod as sort of a guide. The idea here is to just touch the bottom of the slot, and definately DO NOT WIDEN the slot!! It only took a couple of laps to do this on each slot. The rocker/pushrod was reinstalled, and since it was hard to see, I used a flashlight in the lifter galley to see if there was enough clearance between the slot and the pushrod. If the light showed through, the clearance could be seen. I rotated the engine over to check this throughout the movement of the rocker. When I was done I cleaned everything up with a shop vac and carefully removed the tape and rags. I installed the intake, restarted the car and no-noise! After it was warmed up I changed the oil in case I missed any metal chips.
This mod was well worth the effort, I could clearly tell the car had more midrange than before, it was a $100.00 well spent.

http://www.fl-thirdgen.org/blacksheep-1/camaro.mov