Scored a couple of reportedly NOS 289 carbs from The States, a matching pair of 1 1/8" bore numbers that match the '57 Tiger 100 Delta Head exactly. The thing that resembles a dog turd in the middle is a modified SU float chamber to act as a remote feed to both carbs. It hangs from a rubber isolating bush with a fine adjustment stud in the top. Don't know diddley about setting this sort of thing up, other than the float level is critical and must be equal at both main jet blocks.
Going to be a voyage of discovery this, any help or suggestions from anyone who has walked this path before will be more than welcome.
Both right handed, don't know if a left handed version was ever an option.