Something concerns me, here. Is that the main battery cable you have pictured? I would not do that. If the feedthrough is strong, I'd use it for the main termination, otherwise, buy a good solid junction and terminate the main cable, then use a second cable to jumper over to the feed through, and use a SMALLER cable to jumper over to the starter relay. Depending on how large the alternator is, and how it's wired, the jumper to the starter relay doesn't need to be over 8--6 ga wire
(The only thing holding the starter relay stud in there is the small ears on the case and the thin insulating "cover" for the relay)