I haven't built the Soapy Sales version yet, but I recently completed the generic Model King version of the same kit. What is the body/interior tin hanging up on? Do you have a Dremel drill with a grinder bit to maybe trim away the area that's catching? Maybe a picture of the problem area might help diagnose the issue.
Great story, LeRoy! During the recent NHRA event here in Arizona, I talked with Big Jim's driver John Hale. He introduced me to Jim's granddaughter Johnna. Unfortunately, the model wasn't done yet, so Johnna gave me her email address so that I could send her pictures of the finished model. She will forward the pics to Big Jim. I'm waiting to hear back from her.