Running an output through a 4-track can make some nice overdrive sounds. If you want to go the pedal route, Mid-Fi Electronics sells the Demo Tape Fuzz.
I bought a ProCo DB4A at Goodwill for super cheap, but have yet to try it on any eurorack. Four I/O makes for easy stereo setup, and dementionally, it could sit right under your 104hp case.
I also have a Bellari MP105 tube preamp that cost next to nothing. You can buy them super cheap (I think I paid $25 for mine), because as far as mic preamps go, they are very noisy. For warming up/overdriving instruments, they are very nice. It essentially just runs you signal through a 12AX7, so switching out the tube with a different brand or something vintage can provide subtle changes to the output. Since they can be found for cheap, a stereo setup is pretty easy.