I could be wrong, so don't go buying a new can off the 'net on my word alone, but...
IIRC, the Triumph 3->1 header should work with a stock Triumph (or aftermarket, for that matter) right-hand silencer.
You also might get better responses to this query over in the
Vintage Sprint forum. That seems to be where they've exiled the sporty 885 carb people. :wink:
HTH,
-Kit