You can only copyright EXACT layouts and circuit boards. ( The boards would be considered artwork. )
You can only patent something that is unique, innovative and not obvious to someone that is schooled in such areas. Study your Fuzz Faces and Tone Benders carefully.
And something very important to consider is that the information in a patent is public. The use of said patent is controlled by the patent holder.
Consider that the 5 knob fuzz is a trade mark/trade dress issue in the layout of the box. This means that the mechanical aspects make it recognizable even though function has nothing to do with said mechanical design.
I think alot of the concept of the unit question. But it is not patented.
Simple, don't copy exact circuit board artwork and layout. Don't copy the exact enclosure specifics.
( Another link that is interesting about reverse engineering. Full disclosure, I used to work for IBM, this story was legendary amongst certain engineering circles.) http://oldcomputers.net/compaqi.html
I tried making this and the Woolly Mammoth, I fucked the wiring up on both of them (only to pots/switch/jacks) and haven't got round to fiddling with it since I got back from uni, good luck with it though man.