Anything seat belt related should be 7/16-20. I think this is where the jump seat belt mounts, I am going to install seatbelts in the next few weeks so need to figure out exactly where mine go. Any of the auto parts stores will have this size as does seat belt planet. There is one standard bolt...
‘72 is a pretty unique harness. It’s not like the pre’72 at all. Newer style fuse block with plugs but old style headlight circuit. There are some single year gotchas too. If you need any pics let me know. Curious as to what Coolerman says. He does make the replacement wiper and rear harnesses...