KA272/2  Speedo Gearbox 2:1 Ratio - Smiths BG5330/287 - UK Made under License from Smiths Industries, correct 3/4" Dia Centre Hole and Cable Drives from the Top of the Gearbox, unlike the Emgo ones  
You may need to use KS61/3 Rear Hub Retaining Ring - 2 inch Dia x 0.845" Deep and KS62/4 clamping sleeve 1.08" & KS52/4 distance piece 1.1/2"