Jarv .... i can confirm that your middle shaft spline dimensions are correct as shown above! Your proposed sprocket ratios: 48/21 = 2.286 is mid-point between the following pulley combinations: http://farm4.static.flickr.com/3193/3099078185_4f62bde032_o.jpg 70/30 = 2.333 48/21 = 2.286 70/31 = 2.258 The...