Before anyone can give you some help on what to do, let's take a step or two back and find out what you're starting with and where you want to go. You say you want to put a Mach 1 cluster in your Fox dash. What kind of Fox, an '87-'93 aero or a '79-86 Four Eye? I've never done it so maybe someone else will chime in and tell you whether or not the Mach 1 cluster will even fit the aero dash. It definitely won't fit in a Four Eye. Are you going to keep all your underhood wiring and adapt the Mod Motor to it, or are you going to use all Modular wiring under the hood? If you go all Modular under the hood, that makes connecting to the SN-95 dash wiring a lot easier. Assuming the cluster fits the dash, you still have to connect the dash wiring to the instruments, lights, heater, etc., and then connect that to the rest of the car.
Regardless of which way you go, you'll want to keep the cutting and hacking down to the absolute minimum. And whatever you do, WRITE DOWN what you did so you can troubleshoot it and fix it in the future.