[chris32]

You can, but it would be better to ground to the engine block. On some older Chevy cars they had flat metal straps from the firewall to the valve cover bolts to help tie the body to the block for improved grounding.

 

[chris32]

Braided wire is best (10 gauge works good). The straps I was referring to from the firewall to the motor on the older Chevys, were braided copper straps. You most likely you have body to frame ground wires, but as pointed out earlier, if not a good grounding system is worth the time.

https://www.autozone.com/miscellaneous-non-automotive/electrical-wire/bn/4294962085