If you just want slightly more "round" but still a bit nasty, easiest mod would be to change the output stage to a mosfet - with only a slight rebias needed. I.e. change the R6 to something like 240-270k (or use a trimpot), R8 to 4k7 and R9 to 1k5 - which should be generally valid for the likes of BS170 or 2N7000.
Note that I didn't test that in this particular fuzz, but I see no reason why it wouldn't work ... I used such a generic mosfet stage elsewhere and it's pretty trivial to get it to work.