Exactly what I'm talking about. He probably needs smaller ones than those and the brass ones. Totally exists, I've used them for very different applications. Not at the local lumber store. Maybe McGuckins in Boulder, maybe.

I think attached loops would be weaker.

Yes a loop is stronger, about double. That's completely dependant on the swages strength. It wouldn't change regardless so it's unnecessary.

This is the sort of thing to do for a 4 person tandem or some other crazy fun. Not something the OP can or should do.

As for strength, judging by the absolute weakest scary aid only climbing gear, those bits have really similar diameter cable as a bike cable. Swages on those achieve 2kn or a little over 400lbs. Terrifying when you're hanging off it. Not bad if all it needs is to move a derailleur.