So Belair is your setup like stock with upgrades at the moment ?
1. I have a 12 bolt (originally from a 67 Camaro) that is the same width as stock. 60" flange to flange, Moser 33 spline spool/axles/C-clip eliminators, 4.88 gears. If I were starting with a new 9" housing like you are looking at, I would consider asking them to make it 2" narrower overall just to make installing the wide tires easier. Possibly 3". It can be a pain due to the low hanging quarter panel on our cars especially when you have larger/longer wheel studs in the way too. Also a deeper wheel dish just looks good.
2. My upper control arms (2) are UMI adjustable, but again if I were buying now I think I would go with Air Ride's adjustable uppers that have a rod end at the chassis end and bushing at the housing vs. both ends bushed on the UMI's. I had some upper chassis brackets fabbed that give me 2 more positions below stock to lower the front of the upper control arms at the frame to change instant center. Global West sells the brackets for a good price. They also sell the housing bracket for the additional arm.
3. Lower arms are Metco aluminum. The spring mount is removable. There was a good sell on them back when I bought them. I think they were $270 shipped or so.
4. QA1 adjustable coil-overs on a custom crossmember that is a bolt-in and requires no permanent mods except welding brackets to your housing for the shock mounts.
5. Single Adjustable panhard rod. Don't buy one of these. Get a double-adjustable one so you can center the housing without having to take the bar loose.
Out of all of that, the only things you really need to run big tires for just the look is the adjustable panhard rod and possibly relocating the housing back an inch if you want wide tires taller than 28".