1) You don't need to drill the slide; it has nothing to do with jetting (only a change in throttle response) I have KLX jet kits in both mine and didn't drill the slide. If you do decide to drill; go 7/64ths not the 1/8" that is sometimes recommended.
2) the 22 cent mod is OK.....for the price but consider a KLX kit (available from Eaglemike) to properly rejet.....especially if you don't know what's currently in the bike.
....and yes, screw the jet all the way in. ;-)
FWIW, my two bikes have identical jetting, L-mod and silencers; KLX kit, needle on second clip, no washer, 2 turns on the fuel screw and a 142 KH main jet.....jetting is spot on.