Bottle Rocket - I am sure you know for the ACDC tone, gain/distortion is not what you need it is the eq and the open chords. The Crunch Box has the eq but alot/too much of the gain so I use it set at 8 o'clock as suggested above. (I have to brag that I just got my tickets for the Melbourne ACDC show this morning)
Importantly, in addition to the above, I also have my les paul volume down to 7 or 8 o'clock to fatten and clean up the sound at the same time.
As an aside, given this is a Boogie forum, has any one seen the videos in the ACDC box set that show the lads using Mesa Boogies, circa 1984. To this end an ACDC sound on a Boogie is possible!