Welcome Lotus - congrats on the forthcoming addition! Can't wait to see some pics of it when you get it.
Only comment I have is regarding the current owner's single master cylinder with a disk/drum brake set-up. It sounds as if someone started and didn't finish a project - might be a good idea to get a dual master cylinder on there so that you can properly proportion the braking setup you're going to inherit (if you pan on driving it right away before you get to the dual/power set-up, etc).
I'm sure others will chime in on the rear end and/or 6-5 lug conversion options. Here is a link to a place where you can at least browse a whole bunch of options (CPP) even if you don't end up buying anything from them. It's fairly expensive high end stuff (from my wallet's perspective) but it's a huge selection of options on different gear and the link is all for 60-72 chev, specifically. Can at least help give you an idea of what's out there to even look for. I use it as a good place to start and then you can compare from there as you expand your search. Some other folks can help build the picture for your options from an OEM gear perspective much better than I can.
http://www.classicperform.com/6092chevtrk.htm
Welcome again!
jocko