89silverado3500502bigblock

So look. Tomorrow I'm going to pick up this 1989 Chevy Silverado 3500 extended cab and chassis. They allege it has a 502 big block in it but I'm doing some research online and cannot find anywhere where or when they put a 502 big block in factory trucks. Did any trucks around that time come stock out the factory with the 502 or is it a better possibility it was put in after the fact? Last thing, I can't find anywhere a 89 Silverado 3500. It's all K3500 or C3500 and a couple others. I'm assuming in this situation it would be a K3500 correct?