If the car is frame connected, grounding to the chassis should be fine. I do all myu cars grounding to the frame using 1/0 or 2/0 cable from engine to frame. The frame has a nut welded on and is bolted solid. The rear of the car is same. Nut welded to frame and bolted solid. Never had a grounding issue using this approach.
If running EFI/computers or other ground sensitive items, run a secondary cable forward to a buss point and ground there. This is to try an isolate any noise that may be in the chassis gffround from everything else grounding there.
I build most all the cable to spec order. The relays and ford solenoid are easily found or I can get them for you as well.
This is how I do my cars. Nothing is hot in front of the battery tray when the master switch is in the off position. If you aren't racing it and don't care about killing power on the big cables, plenty of other options can be done.
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Just my 2 cents.
