Mach 1 slp catted s w/ lt???

well i saw this ad here in stangnet where someone is selling catted x-pipe only made for longtubes...

myy question is can you do that??? put cats with lt..

p.s... Still waiting on suggestions ona what i can do about my p0420 code that keeps popping up...

cat effficantcy below threshold in bank 1???





thanks for the help