68 dart sports special update and questions about rear.

It's been a while since I posted on here. I had a knocking slant 6 in my 68 dart, but my dad and I pulled his 383 from his 67 belvedere as I needed an engine that doesn't eat oil so fast for school. Rory Fontana swapped the 383 in my car in late August - October 2017. We also had a 727 rebuilt to go with it along with a 489 rear. My dad will probably see this post and be able to answer more questions if you have any lol.
When my dad and I rebuilt the head on the slant 6 (before we knew it was a bad short block) we also did a disk brake swap in the front using the scarebyrd setup. However, I was never able to get a firm brake pedal with this set up, and the shoes in the rear wore out while I was on the freeway last month. When this happened I had practically no pressure at all in the pedal and it was something I didn't want to go through again. My dad and I decided to swap out the front brakes with a 70s factory disk setup and it's been perfect. I now have a firm pedal and it just gives me a lot more confidence driving the car.
The 383 has been a lot of fun so far. It was installed using the transdapt motor mounts and Schumacher headers (I kept my power steering). Rory sold me a small block radiator to cool the 383 since the slant 6 one wouldn't be enough. The engine seems to usually sit around 195 while moving and will climb to 220 if idling stationary for a bit. Eventually I'd like to put electric fans on the radiator and have a separate cooler for the trans, but none of my gauges work (I measured with a temp gun), so I don't want to swap in electrical parts until I have a way of knowing if they fail while on the move.
So far I've been driving the car frequently to and from university and work while I study math with the goal of becoming a high school math teacher.
As of right now, I wish to have the rear end rebuilt since it gives a terrible noise when moving (the rear end sat outside for a while), and I was suggested that it's probably the bearings. While this is getting done, I also plan to have a sure grip installed in the car and 3:23 gears. I also would like bbp axles installed, since I already have bbp in the front and the rear end came with sbp (wish me luck in case I get a flat), and I would like to know what else this will require. When my dad and I changed out the rear shoes 2 weeks ago, the backing plates didn't accept 1-3/4" shoes. Instead, we got 2 -1/2" shoes for a 67 belvedere and they slapped on perfectly. I'm wondering what else will need to be installed with the bbp axles, if anything. Also, after this swap, does anyone know what width 15" tires will fit in the rear? I'm hoping to put at least 7s in the back and 5-1/2s in the front. I don't want to cut anything up or move the springs.
Thank you for any experience and wisdom you have to share. I hope the update was an interesting read and that you enjoy the pictures I will be adding shortly.