I mounted mine on the frame rail under the battery. I cut a piece of metal drilled some holes to match some of the threaded holes in the framerail, mount the box to the metal piece and bolted it in, never drilled a single hole in my car.
I got mine on the firewall. exact middle. Drilled four holes screwed it on. Fired her up and love the location. Oh yeah, mine IS carb'd and the relocation is going down whenever summit delivers the goods. Waiting for parts is worse than waiting for christmas, swear to god.
mounted mine where the battery was along with my ballasts for the hid headlights gave me a good reason to move the battery to the trunk...used the stock battery tray and screwed it down i have a different coolant resevior so thats y i couldnt move it to the pass side fender