well if your gonna use heli coil, which i would also highly suggest, your gonna have to tap it out larger to compensate for the thickness of the heli coil, so that the 02 sensor will still fit. I think you will have to tap it out 1 size larger than it should be, put the heli coil in, then the 02 sensor. Also another good idea might be some never seize on the threads of the 02 sensor if it doesnt already come with it. It is suggested and will be a lot easier removing it next time around if you have to. ...just my 2 cents...
1995 Bonneville SSEi:
(still without a motor and tranny) 15.606 @ 87.95mph (stock)
1998 Regal GS:
DHP 1.0, JMB FWI, ZZP 3" DP, 04 GP 12" Brakes, ZZP 180° Drilled T-Stat, SLP Single Outlet Catback, Silverstars