They don't seem to be compatible? let alone stem diameter or length.
Triumph 1300 Early
Triumph 1300 Late
Current fleet: Triumph Dolomite Sprint '75, Daihatsu Fourtrak, Honda CG125, Yamaha Fazer 600, Shetland 570
Disposal fleet: Golf GTi 16v MK3 Anniversary
Past fleet: Triumph 2000, Lancia Beta Coupe, BL Mini Clubman, Austin Metro, Vauxhall Cavalier MK1 & MK2, Renault 18 D, Rover 216 GSI, Honda Accord (most expensive car purchase, hated it on pickup from dealer, was made out of magnetic metal as only car I've ever been crashed into, 4 times), Golf GTi MK3 16v x 3