Grinding a slot is an attempt to bleed off air that's trapped in the oil at sustained rpms, as these engines when running hydraulic lifters tend to bleed out and hammer.
Grinding a groove on the outside of a lifter will do nothing for a cold start ticking.
You should be running 3/4+ turns...
Have you resurfaced the tips of the rocker arms? This can reduce much of the noise. I run solids in my 261 and I have less noise and NO bleedout problems like I did when I used to run a hydraulic cam in my old 235.
If you can accurately identify where the noise is coming from, you could try replacing that lifer. Also checkout the condition of the pushrod ends, and the adjuster balls.
The best thing to do is run solid lifters in any 235 or 261. With the rocker assembly in proper condition and proper adjustment, you will have little noise and no worries.
