At risk of sounding like I work there, you might visit your local Discount
Tire/America's Tire Store and take your truck with you when you go. You can
also consult your local custom shops and maybe even a speed shop.

You have a couple of issues to go over. You want tires and wheels that fit
the truck and look good together, but you also want different size rims for
the front and back that are also the same style. You also have backspacing
issues that you need to know and understand. I suppose you could find that
by measuring the stock (or whatever) rims you have now, but the tire guys at
the store will know how to do this, and then show you pictures of rims that
meet the spec.

When I was a kid, my dad had a '65 Ford unibody truck that my dad fitted
with different size tires front and rear. It looked cool and worked well,
but I don't recall the sizes we had. I don't know that the sizes would be
useful today because they were something like F78 on the front and L78 on
the rear, and I don't know how to convert that to the way they size tires
today.