[Ol' Ron]

Yes, by all means, drill the adjustment holes. Buy a 3/16 long drill at a hardwarre store to make the job easier. Drill the hole just above the oil tube. Make sure you knock the bore off the inside of the lifter boe. I use a wheel cyl hone. Also for those using a hi lift cam, grind of about an 1/8" off the top of the lifter bore, so the wrench will fit..
All this does is to make sure you do more than one flathead