Seanoss
They have been doing Victacode well back into the 60s
You are correct; the square housings came in in 1976 (CyberJack may be able to enlighten you more as to whether it was 1976, or the upcoming 76 season if that makes sense - ie late 75)
The square housing with integral throttle lever came with the G4 carburettor which replaced the G3 at that time