Shane, I drilled my old mids just above the lower units, there is a lip where the end of the exhaust basket narrows and goes into the lower, you need to pull the powerheads, remove the inner basket if you have one and drill about 5 to 6 holes on each side, do not drill holes anywhere on the back of the mid section, as far as performance, it sounds good and does let the motor breathe alittle better but I didn't see any performance gain. Are you coming next week or what!!!!!!!!!!!!!!
Give me your # I'll call you if its ok!
As far as the size I think I used a 3/8 inch drill bit