Well, with my '78 60/100 EQ Mark I, I used a Boss OD-1 with the level wide open and the drive nearly cut off. I think you could get by with this trick on a HB, but you might also need an EQ pedal in the loop. I used my EQ to add back in some of the bass that the overdrive pedal choked out. My amp had the "post-FX level" mod like is done to some of the IIB's and the EQ was moved in the circuit (after the preamp) like a Mark II. 8)