I think the slimline and wideline frames use the same muffler bracket: part # NM25190
I made mine, based on what was required to get the exhaust sitting in the right spot.
The link below has an overall length, presumably finished.
The inch dimension provided must be incorrect.
You can scale the width from the given length. I used 3/16 inch thick stainless stock, which was probably overkill, and needed heat to do the offset bends.
25190 RGM NORTON
www.rgmnorton.co.uk