RE: .21 in T-Hull proboat LLumar
Yeah, you need to whack off 3" there and it should run much better. You can remove it from both the pipe and header to get the length right. A tubing cutter does a nice job.
If you ever find that you went too short then you can add length with a tuned pipe coupler. You want a little gap between the pipe and header anyway so that they don't make contact.