Most likely what is happening is tha wheel is hitting the brake drum on the outer fins of the drum. I had a similar situation a few years back. My brother-in-law had a flat on his Blazer, but no spare. Well, I let him use one of the tires from the '55 as it was bare frame at the time. The wheel wouldn't clear the drum.
If you want to keep the stock appearance, you might consider using a 16" wheel, otherwise you'll need a wheel from a '73-'87 4x4 to clear the drum.
