BTW- for any one out there contemplating such a project or for any one using teflon couplers to couple their exhaust system and have not been happy with the leaks, here's an idea that might help.

You can build custom couplers as I have done. You can build in any sort of angle or diameter mismatch you may have. Here a how to:

Get a small quantity of ceramic cloth from any decent source. Mine was McMaster Carr. 6oz. glass will probably work too except go 3-4 layers. Cearamic is thick and fluffy
Get some Permatex Ultra Copper hi temp gasket maker for gasoline engines (also from McMaster, but there are many sources).
Set the header/canister/pipe pieces exactly the way you want them.
Line the attachment areas of the stems with plumber's teflon tape. The lining keeps the silicone from adhering to the aluminum
On some scrap plastic sheet rub the Permatex Ultra Copper into the ceramic cloth. You want enough cloth for two complete wraps. Wear gloves as this is a bit messy. I use a small seam roller for wallpaper
Lay the wet cloth over the header/canister stems and wrap the work with more plumbers tape making sure you pull everything tight. Let cure for a few hours or 24 for full cure
The teflon tape peels off easily leaving behind a very nice finish
Twist a bit to separate from the stems and voila!

If you want some exhaust stingers do it the same way except use so 2-3 oz glass cloth and rub the silicone into the weave as well as necessary to seal it. Wrap 2-3 layers over the size tube you want. Make sure to teflon line the tube mold first.

BTW- the DA flex header I used on my DLE55 eventually burned through the teflon tape that lined the flex area, after around 70 flights or so. Started to sound like a kazoo. The flex area was repaired the same way with one wrap ceramic cloth and Ultra Copper. Still going almost a year later.