That Range-Master would fit the bill, but it doesn't have tons of gain like a Fuzz Face. You could built a Schmidt trigger type fuzz in there without a lot of parts. One 741 chip, five resistors, one pot, three caps, input/output jacks, and a SPDT switch would be all you'd need. Radio Shack doesn't have the type of switches you'd need; they're a bit flimsy to be stomped on. Not true bypass, but the input impedance on a opamp is infinite (in theory) so it shouldn't load the signal too much, and I figure you'll be using it in the studio more than on stage, right?
I'm thinking a non-inverting opamp stage with a gain of about 1,001 (gain is always 1 + R1/R2 in a non-inverting circuit) one pack of 1M and one pack of 1k would do the job, as well as a 100k audio taper pot. If you wanted adjustable gain you could get a 100k linear pot (don't know how you'd get everything in that little box) for a fuzz control. Also you'd need one of the little 1.75" square PCB boards RS sells for IC circuits. These come two to a package with a break line in the middle of the board, but don't break it - saw it. I've tried breaking it and the results weren't pretty.
I'll play around with my breadboard and see what I can come up with.
Is it the small size MXR box, like a Distortion + comes in?