I'm putting 2.02" valves in 360 heads ...

I machine heads, do not drill out guides with a drill bit!!!!! you have to use a guide reamer , made for this job!! the reamer has a smaller end on it, goes into guide and keeps it straight as it cuts. also, have to have a driver that fits the reamer, can be used in a drill motor. a drill bit is for making holes. not for doing guides. something to consider.