Try a different muffler shop. I had purchased the Walker pieces but wasn't satisfied with the way the bends looked. They had a lot of ridges.
Stopped by my local muffler shop. He had a "recipe book" that told him where to bend some new pipe. He bent both pieces and it fit great. Best of all, his prices were cheaper than the Walker pipe from Autozone. He handed me the pipes and I did the installation myself at home.
I did end up making the down pipe shorter so the exhaust would tuck up closer to the frame but that was no big deal.
Here's a
link to some pics on my website. 1965 short stepside.