1; Yes, it will ride smoother. Straighter, not so much, as that's more of an alignment issue than a tire issue. 2; The only tire that will work on your existing wheels are the 17.5s. You will need to get replacement 16 or 17 inch wheels to use modern radials. 3; You'll want to look for a wheel with no more than 3 1/2" backspacing. There recently have been 8 lug 16" wheels released on the market, they may be worth looking in to.
Since you're loking for a lower profle tire than stock, I would suggest an LT245/75/16, which will maintain the proper load range to support the truck.
