I’ve just spotted this post. Yes, I made a ’27 system for my long frame Flyer about 4 years ago from a drawing provided by John Underhill. the drawings were in the form of a set of A4 photocopies (which I still have, although they’re a bit oily by now) patched together with sellotape to make the full size drawing. I’m no engineer but managed to cut & shut the various parts & got a local welder to assemble them. The tailpipes curve under the frame & turn outwards at the end and were bent by a company in Coventry & subsequently nickel plated. The end caps I turned in aluminium. The downpipes & pepperpot I painted with black exhaust paint which has largely disappeared now & it’s beginning to look scruffy. I had a lot of trouble getting the various joints to seal as the pepperpot distorted somewhat during welding. A point to note is that the drawing that John provided shows straight downpipes (which is what I made) but I have since seen contemporary pictures which I think show curved pipes. Perhaps someone else could comment on this. Also, because the tailpipes are quite short and end at the front of the rear rim the back of the bike gets into a bit of a mess, I’ve used Castrol R which doesn’t help. It is very loud and vintage sounding & I sometimes wish it was just a little quieter but I’m told by others that it sounds really nice when “on song”.
If I can help in any way please don’t hesitate to get in touch via PM