Have to chime in on this one (great build, BTW):
I built my cousin a Lead Solder over the summer, wanting to get it right, work out any kinks/tweaks, and then built myself one.
Finally finished it up about a month ago (I always have multiple projects going at one time) and added the crunch mod on a toggle on the side. It works, but there was a different overall sound in lead mode.
The difference between mine and the one I built for my cousin is that the cap used in the my mod was now tantalum, where the previous one was electrolytic. I took it apart last night, replaced the cap with a 1uF electrolytic and dropped the resistor value down to 68K.
This brought back that treble 'sizzle' on tap, when I want it, via the presence control.
Just my $.02, YMMV.