Here's the answer to "how do I do it?"...IMO. I'm wasn't smart enough to come up with the diagram below, I owe thanks to Eric68 for it.
It works great on my car.
The battery cable is only hot when it is turned to "Start". I ran the wire inside the car and passed it through the firewall with a bulkhead connector vs. a grommet.
Also, I put a maxi-fuse on the alternator wire.
Make sure you use heavy wire to run current all those long distances. For my battery cable to solenoid to firewall to starter, I used 1/0 wire. Found this to be and Excellent Tip: You can get good 1/0 wire from a welding supply store. Lots of strands and much more flexible than battery cable you would get at an automotive store.
I mounted the ford solenoid directly to the exterior of an aluminum Jegs battery box and the switch to the side. The handle runs out the trunk and through a pre-existing hole in the bumper. When the handle is removed, you'd never know it was there. At the track I use a marker to write Push Off on the bumper. When I get home I take off the push rod and wipe off the writing. The cutoff in the trunk is also kinda a poor mans security system...although it kills your radio presets. I'll try to snap a pic later.
For ground, I have cable that goes to the back side of the trunk hinge mount bracket. Wirewheel the metal and attach using a star washer. Up front, ground straps from firewall to subframe, firewall to block.
Sean (68RS406) is an electrician...hopefully he will point out any errors or suggestions for improvement.