If your roller cam end play is set by shimming off the front cover, don't touch the water pump bolts or you will be repeating the entire cam shimming job. There's always the block drains next to the motor mounts, I guess.
If there is oil in the coolant you need to drain everything lower Rad hose, as well as the block plug, and oil drain plug. If you just pull the lower hose you can still pull the heads off with out coolant going everywhere. Then just pull the oil drain plug.