Triumph Repair: Pacesetter header clearance..., spitfire, clarence

Question
I am getting a knock around 800-1000RPM and believe it to be coming from my pacesetter header.  My question, is did you notch the frame for clearance?  I have a 1974 spitfire w/ 42000 original miles and the frame is almost spotless, so I hate to notch it.  any suggestions?  

Answer
Hi Bradley,
I do a lot of modification but never had to notch the frame on a Spitfire. But have on other cars. It depends on how much you need to notch it and weather or not you could have the face of the "header plate" surfaced at a slight angle to give yourself a little more Clarence down below. If you would prefer to notch the frame a little just to get enough clearance to stop a rattle, you should weld in an arched plate back in where you notch it so as to keep the strength of the frame. Another option when it is just a small amount needed, is to shim the motor mounts to either shift the engine or just one side to tilt the engine a little. That sometimes works without upsetting any thing. That might be a better option for you since it sounds like you only need a small amount of clearance added.
Howard