[vectorit]

With out doing a chassis swap from a newer truck, so that you can get the modern brakes and suspension.

The thing I would focus on the most is the brakes.
If you go 3/4ton, you can upgrade to a 14 bolt full floating axle. These axles have giant drum brakes on them.
For the front brakes, if two wheel drive you could upgrade the size of the discs and new calipers. But you may run into issues with wheel diameter if you want to keep the stock looking steel wheels.

Interior wise, you can install shoulder harness seat belt on all three benches. Minus the seating position next to the 3rd door.

Old cars/trucks don't have all of the modern safety as a new vehicle, since they are running what was considered safe designs of the time. Retrofitting modern safety equipment into a classic is a whole costly project in itself.

I know in my 1968 Suburban, I only drive it at 1968 performance today. Meaning I do not travel faster than 65 MPH, and I keep a very large buffer between me and other cars.