Berlin

Yep, Most systems use some of the original headers anyway. The only restrictive part is inside the tube that connects the end can. There's a perforated lining tube in there that is omitted in full and 3/4 systems. The front header has no restriction but may benefit from being tapered or a slightly larger diameter if seeking absolute power.

The Leo Vice, Hindle systems are featherweight but cost a lot. There's a Jardine 3/4 systems for sale on here that uses the original front header.

If you go to a twin can set up on a race bike you have twice the weight and twice the cost if (when!) you bin it.

A lot of extra cost for no gain.

C