no need to apologize. JR is one of the few people i have seen who note the grounding upgrade is necessary (just as upgrading the 'power' side is necessary).
were it me, i would get some bulk 4 gauge wire (stereo shop, online, etc) and make my own cable. alternatively, you might be able to go look at the battery cable section of the parts store and find something that will work (needs to be long enough and have a means of being connected - some cables have an eyelet at each end - great for putting a bolt through, a la how the cables connect to the starter solenoid.
JR might know of a better way to do it - this is how i would (the extra ground, while important, is not as finicky as a power cable. it is hard to mess up a ground cable.

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good luck.