Tires: what size tires?, chevy silverado, wheels and tires

Question
I bought a '88 Chevy silverado pickup that has the wrong size wheels and tires on it. I need to know what size of rims and tires I need to purchase. It's 5 lug, ext. cab. I just want tires that will get me around on paved streets with an occasional trip on the freeways. I'm thinking of buying used tires or recaps and would like advice on that as well. The truck will be used for short hauls and pulling horse trailers if that is of any importance.

Answer
Is this a C 1500, C 2500 C 3500 K 1500 K 2500 or a K 3500?  2wd or 4wd?
Let me so I can finish answering the question.
As for the rest of the question, never buy recaps unless you want problems.  They are a waste of money and do not last nor give you any good traction.  Used tires should be the last thing to think about.  Used can be problems.  Remember they where used and you do not know how bad they where used.  Therefor they could blow out on you.  Any type of hauling and even pulling a horse trailer should involve new tires for better traction, better handling,  better stopping and handle the weight of the load.  Used tires have worn sidewalls that can make them weak.
John