55-59 - Want to do interstate speeds

[yossarian19]

I've got a '57 1/2 ton longbed.
I put the outside-the-frame power steering box on it, tapered roller bearings, 12" front disc brakes, new shocks, new kingpins, replaced the worn out bushings - and it's still like steering a boat at 60 mph.
Will a front / rear sway bar kit make interstate speeds more manageable, or am I at the limits of what I can do on the original leaf springs & beam axle suspension?
If the $250 for sway bars is going to make 70 mph a safe and reasonable speed, then I'm all for it.
I'm not interested in spending $750 on new leaf springs, a drop axle or anything else but a 1/2 ton IFS with big brakes.
Just wondering what I can expect from a sway bar kit - because if it won't get me "there", I'll save my money for a Crown Vic or Dakota or C10 setup.