What size tires for 65 C10 230 6cyl?

[72step]

I am going to be needing to get at least some better used tires pretty soon for my project 1965 C10 as one of them is always flat. My question is what size should I go with? This truck currently has 6 lug 15" (not rallys) wheels off of a 1985 Chevy K10 with whatever original size tire those trucks came with. I'm likely going to stick with these wheels and would like some ideas as to what size of tire would keep it close to original? I'm thinking I might just paint them red and install chrome lugs as I like that look and I might do the truck satin black. I would consider the original hubcaps but I'm pretty sure those are clip right and wont' work on my wheels right?