Generally, yes they will. That said, you might not even be able to find an original style any longer.
If yours is actually original, aside from being part miracle(!) it will have a spring-tensioned upper rod end at the steering box/pitman arm end.
Those were not even available starting nearly 30 years ago, but I haven't kept up on that, so don't know if anyone is either reproducing them, or has found some old rebuild kits on an old dusty shelf somewhere. Maybe eBay will be your friend on this.
Otherwise, pretty much EVERY aftermarket version is going to be beefier and have less play right out of the box. Going with "sotck" replacements will likely be slightly better, but true aftermarket upgrades are usually larger diameter, and sometimes even use better materials.
But none of them will retain that original appearance.
I would not at this point anyway, dwell too much on the originality, since you're already body AND suspension lifted, with tires that are not even remotely the same as were original. So even with uncut fenders (are yours still original here too?) it no longer has all of it's mechanical originality.
Steering boxes are available, but no longer new unless, here again, someone has started reproducing originals. Old ones can be rebuilt, but some seem to have varying results. I bought a brand new one from Ford in about '80 or so, and was shocked at how much better if felt than my only 9 year old original. But those days are long gone I'm pretty sure.
Which is one of the reasons we (Wild Horses that is) dwell more on the new and rebuilt power steering upgrade systems. They're far from original (though we have those too sometimes) but they're better, so "original" is not as big a deal when you're looking for more fun driving it. Especially with larger tires.
But no matter what, definitely do the test that was described above. Leave the full weight of the vehicle on the tires and on the ground. Don't lift it up to inspect. Just use the power of the steering wheel to torque against the weight of the truck. This highlights anything that's loose. Just about anywhere on the whole vehicle!
Have fun.
Oh, and we'd love to see pics of this (presumably) low mileage(?) '66 you've got! We love pics, but especially when there might be something special to "I spy" underneath or under the hood.
Do you know what month it was built in? Have you drilled down into the VIN to see what other info you can find out? We've got a great thread here somewhere that is keeping track of the early '66 models that are known to exist.
Hopefully it's still got it's data plate riveted to the driver's kick panel. I know others would like to see what info is available.
Paul