The B71 boss is available in narrow or wide back versions with the latter listed for your car. Note also MotoLita only seem to refer to 4/4 models for later cars so the year seems to the more important. If the narrow back version would fit (same splines I believe) then an alternative would be the B71J below which is the one I have on my Roadster.

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Might be worth a chat with them.

Richard

2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone