[dsraven]

ok, my 2 cents.
if you like the truck but hate the cons (loud, bouncy, underpowered, poor shifting, std strg and brks, poor heater and wipers, slow on the highway etc) and are looking at a newer version of the same thing (from the 60's), except possibly power steering, brakes and more power, then do a little leg work and find out what it would cost to do the mods to the old truck. seriously price it out at worst case scenario. they make bolt in ifs cross members that you can install yourself and have rack and pinion but you will need to modify or replace the column, brake system etc.
you can scrounge some parts off craigslist or buy a wreck that has the engine/trans/diff/steering column you want, scrap or sell what you don't need off the wreck. the other method is as mentioned, buy or build a frame and drivetrain you like and then stick the old body on top when done. you still get to drive the old truck in the interim. the frame is pretty flat so you could even build one if need be. I would not opt for the camaro clip method, personally, because they make so many decent bolt in ifs systems.
the other side of the coin is to sell it and spiff up your daily driver, which hopefully has all of the above along with upgraded safety equipment for the family. the second is what I did years back. now the family is gone and I wished I had kept my 58 fleetside in a garage somewhere because what I could find for a project nowadays is really rusty. wives usually like the newer, better riding, quieter drivers, that they can also drive and feel "cool" in but feel like it won't leave them stranded somewhere. my wife was more apt to spend money on a daily driver to make it cool than "spend more money on that old thing again".

anyway, in my opinion (and possibly your wife's) you would simply be
swapping years and body styles by selling and buying a newer version from the 60's. still gonna be a want list, still gonna be noisy, not gonna have the safety equipment to haul your kids around in (not sure of the ages or if car seats are a factor) and it's gonna be sitting there begging to have money spent. all that aside, if you are ok driving it as is, keep it. upgrading the axle to something with discs won't make it ride better or steer better unless you add power steering and then you will need to assess the rest of the steering system, springs, spring pins and bushings, shocks etc. the frame mounted p/s box from the 70's era trucks, that some use on these trucks with a solid axle, will reduce the steering lock to lock turning radius because the tire rubs the steering box when tuirned all the way to the right. the box is mounted to the frame ahead of the axle centerline, so if you go with the other style of box that, mounts where the old box was, you get full turning radius but it is more costly.
what I am saying is, do a complete feasability study, include the wife in the decision making process (yep, cash spent affects her as well), consider the safety issues with kids riding and decide from there.
your truck looks to be in pretty good shape but could still easily go past the 5g budget.
write down what you want to do with it and how much you want to do yourself
price out what that will cost
write down what you would want from a different truck
price that out
include the upgraded daily driver concept if that would work for you
price that out
decide
easy peasy right?