The 1M exhaust as you have described needs not just the bumper & diffuser but also the battery 1M battery tray, 1M battery, extended battery leads and the charcoal cannister moved a bit.
I have just done a quad for my 1M conversion check out my build log:
https://www.1addicts.com/forums/show....php?t=1446901
Or for the full 1M conversion:
https://www.1addicts.com/forums/show....php?t=1069755