Thermostat replacement problems

I have a 1996 gmc safari 4.3l v6 w code I can not get a a socket wrench over one of my bolts on my thermostat housing, because of a bracket just above the left stud any suggestions ive tried everything i can think of and so has my father any help would be greatly appreciated.

Also where is the drain petcock on the radiator?

You'll likely have to remove the three bolts/nuts holding the throttle cable bracket to get clear access to the thermostat housing bolts.

The petcock should be located at the lower right (passenger side) corner of the radiator, near the bottom of the right tank.