First, this car will not be kept all original. This isn't "vintage restorations.com". It is a very nice specimen to work with as there is no rust. One of my first cars back in 1964 was just like this, which I drove in stock form for 3 years.
The 216 babbit pounder splash lube six will run forever putting around town, but just does not cut it on the freeway at 75 or in mountain driving. The ball bearing front hubs are very susceptable to miss adjustment and don't last at all like Timken rollers. Likewise the original suspension and steering has a short wear life and gets sloppy so is not good for freeway cruising in comfort.
As for brakes, I've had an S10 Blazer and the brakes were a headache. The blazer brakes are 'bout the same size as the Camaro but the car is heavier and the wheels are larger. The result is they would often overheat and burn or warp the disks comin' down the mountain. The '48 Chev is a fair bit heavier than the Camaro and will have larger diameter tires (closer to the originals). So I value bigger brakes.
I realize that Mustang II and Camaro/Nova suspensions are most popular for old car upgrades. Both of these options were designed for lighter cars. So you can get aftermarket upgrades for brakes and dropped spindles etc. but I see more $$$ this way. I like factory junk yard parts that will do the same job. So maybe Ford LTD or Chev P/U or ??.
As for the twin I beam, I'm aware that there is a lot of controversy over this suspension. I've heard that on a van the tire wear was horrendous. I've also heard from a P/U owner that liked it better than his Chev. I figgur that a change in the ride height from loading the van in particular, where more of the load can be on the front axle will result in camber and toe-in change that will cause tire wear. So it may be important to be able to easily sdjust ride height such as with air bags or jacking screws over the springs like the stock car racers use. Also improvement to the steering geometry should help.
I have one other wrinkle to consider. I want to put twin turbos on the 300 six. So clearance between the front turbo and the upper A arm pivot might be an issue.
I'm still open on this. Am looking for the best junkyard solution that has good brakes and readily available replacement parts.