| Like someone already said, this is nowhere NEAR an "overdrive" circuit. In fact you're going to find that it actually lowers your signal output level. Overdrive circuits are used to OVERdrive a circuit or amp by producing a LOT of properly voiced gain, like 20db (at least) or more.
This is a novelty at best. By the time you buy an enclosure ($10) the 3PDT footswitch ($5), the pot and knob ($3 minumum) and the diodes (??) for the results it produces you may as well buy a clean booster circuit ($10 kit?) and create a REAL overdrive (a gain boosting circuit that is used to drive something after it into distortion). Add a couple of diodes after the boosted signal to create some clipping and you'll have a truly crappy distortion unit!
This may be something "fun" to tinker with, but I highly doubt you'll like the results. Diode clipping (when done incorrectly) sucks the low end from a circuit.
In any case, have fun with this. One question, without an LED to tell you when the circuit is engaged how will you know if it's engaged or not if you want to use it?
For super simplicity, you may simply add the diodes inside of your bass, just solder them from the "hot" to the "ground" and you're done. Stick a toggle switch in there to disconnect the diodes from the ground to turn them "off". And remember that they must face opposite directions for them to work.
Don't expect much though. Diodes clip a lot better when they have a boatload of signal going through them, and remember that all of that signal that is going through those diodes to ground is taken from your output .. so your output level will be reduced.
This thing is like bicycle without wheels. Technically it's a bike, but all you can do is drag it around and claim you own a bike. | 
