Roller Block: Pushrods Rubbing Against Head

92 LA roller block with earlier 596 casting heads. Using stock replacement Melling rollers. When trying to find the correct pushrod length, I removed the rocker and and pushrods to find that they rub on the bottom to middle portion of the hole. Enough to leave a bit of a lip of metal. I know there are many threads out there that say that they can be drilled out. I know to get a carbide bit, but which ones do ya'll recommend or which ones worked best for this type of job? Lots of different types out there. Also have a Harbor Fraud electric die grinder that spins to 25k. Thank you!