you won't find a newer style chassis w/ all the bells and whistles that you can just plunk all yer sheet metal on - the usual route is to put some later front clip on your frame and a later rear axle and updated driveline
another alternative is to get a disc brake kit w/ dual M/C and convert that, and get some mono leafs to ease the truck feel - power steering isn't too hard on'em either - piece at a time
or you could buy a newer truck for less money that already has discs and coils and power whatever, and pass the 58 on to someone who appreciates it for what it is!
Bill