i want to fit a 06 gp1 exhaust on my 05 600 and read on one of the forms that if i take a crayon or tire marker and put a line on my header that where it stops burning off after i run it im safe to cut with out changing back pressure or anything. if i do this and make the exhaust from that point back to fit the gp1 will i be all set and not hert my engine?