ECU box ground.

Getting ready to convert my lean burn to a 70's style electronic ignition. I have done this conversation in the past a few times eliminating points. I have always grounded my ECM to the fender well or firewall. I was thinking this time grounding it straight to the battery.Would there be any issues grounding it straight to the negative side of the battery? Or maybe grounding it to the inner fender and the battery?