Gregg,
I agree with ata. Remove the lower radiator hose to drain as much coolant as possible. Back flush with a hose attached to the heater fitting in the head. You will see rusty water drain from that lower radiator hose. The petcock won't let water out fast enough for a good flush.
Buy hose clamp pliers from an auto parts store to get the hose clamp off. See the current TDR, pages 115-116 for Jim Anderson's opinion regarding replacing those clamps with screw-on clamps. Dodge's position is that you need to use the same spring-type clamps, but I can't fault Jim's logic either.
For the full how-to on changing coolant, see my article in TDR #35, page 76. I learned a lot researching for that article.
Good luck.
Loren