I had a bright idea that I could turn the gears down and mount the spindle pulley inside the head, where the gears used to be. The motor would then be sat flush on top of the head which would look quite nice. Changing the belt would be a bit of a PITA but wouldn't be a regular occurrence. However, having drawn the design to scale, it turns out that the motor would foul the top of the spindle. Whatever I do, I'll have to raise the motor above the spindle.

Unfortunately, the O.D. is 45 (6209 bearing) and the I.D is 37mm, so only leaves a 4mm wall thickness. The only solution I can come up with is to use a piece of 50mm stock, turn about 10mm down to 37mm diameter, chamfer the edges, press it in and TIG weld around it. Then I can turn the O.D. down to 45mm and bore the centre out to 37mm. The pulley will have to be bored out to 45mm but that's not an issue as I can select the motor pulley to give a ratio of around 1.5:1. The 37mm bore is not critical as it's only clearance for the spring on the hand feed.