Very confusing thread here since at least two guys are doing a conversion. As I said in post 5 Tom has a quality control problem with his machine work that I found on my '64 kit. Yours may be similar. He grinds down the caliper where it contacts his custom bracket and on one of mine wasn't ground down enough.
My problem manifested itself as a howl when turning left unless I was also applying brake pressure.
Tom told me that the calipers were stock S-10 parts so I got a replacement locally for cheap. When I tried to bolt on the new caliper I found it contacted the bracket in two spots. I then carefully inspected Tom's caliper and found that he had ground them down at these two points, just not enough. The silver paint that he uses on the caliper makes the grinding work difficult to see.
So before you toss out the whole kit and send it back, carefully inspect to see if you don't have a similar problem.