MII is not your only option. You can find 4.11 gears for your rear end, which will be an improvement over the 4.56 gears. There has been discussion about an 8 lug disc brake kit. It is not available to my knowledge yet, but should be pretty soon.
An upgrade from the "huck" brakes to "bendix" brakes will also be like night and day. You can pull the backing plates and hubs off a 53-59 3/4 ton for that upgrade. It's a bolt on change.
A 2 chamber master cylinder with a booster will also help in stopping your ride weather you convert to disc brakes or not.
At the end of the day it all depends on what you want out of your truck. If you like the quirky way a 46 3/4 ton truck drives, keep it mostly original. These trucks are getting hard to find in an original state. Preservation is actually a pretty cool thing. There are plenty of incomplete projects for sale out there that have already been subframed.
