IDK…
You could epoxy a small piece of plywood to the inside of the firewall and mount the fuse box to the factory spot. The wiring could come up through the spot where a factory clutch rod would be.
I didn’t smooth off the fuse box bulkhead on mine. But some spots I added electric components was on the left side of the steering column/brake pedal bracket and above the accelerator pedal bracket. They’re not the easiest to access for servicing but are hidden well and can be removed and serviced with some effort
Here’s the one above the accelerator bracket in its early stages
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Out of the truck showing the bottom side and the thumb screws that I mounted it to the pedal bracket with
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Top side (after I radiused the edges and painted.
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I couldn’t find a good picture of the other spot, it’s basically a piece of plywood that mounts on the side of the steering column support using a thumb screw. I mounted my remote lock and window control box and a bank of relays for the windows and fuel pump.
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ETA: I ran the ECM harness along the transmission and mounted it under the seat