Hi Garry, A word of caution that old lady should have a 1450 rpm 1/2 or 3/4 hp motor fitted with 2850 rpm input you will have warp speed if you use the high speed combination. This could be very nasty,top speed for spindle should be about 28/2900 rpm. It seems like the motor has been swapped at some stage as the original motors did no have a capacitor for either starting or running but sed a four pole 1450 rpm motor with start windings controlled by a centrifugal switch inside the motor.cap start,cap run motors are ok for this sort of use but they need to be four pole to get the correct safe speeds for the lathe and its aged bearings.The pulley on the motor you have may smaller than the original to cope with problem above, an easy way to tell is that both sets of pulleys are a reversed mirror image of each other, ie the low speed set is small motor pulley and big spindle pulley and so on, but both big pulleys on each shaft should be the same size and likewise the rest of them.The low speed set, is small motor pulley and big spindle pulley and so on,to get all four speeds up to big motor pulley and small spindle pulley for high speed , about double motor speed 1450 to2900rpm spindle speed. The weight of the motor should provide enough tension for the belt, better too loose than too tight. too loose means slip, obvious and easily dealt with with a little more tension. Too tight risks knackering very expensive bearings. The motor pulley may well have two allen headed grub screws , one on top of the other to secure the pulley to the shaft, be gentle getting the pulley off, as if you distort the aluminium flanges it will vibrate like a b****r and spoil your work. Link belts can be got from RDG tools and they are very good. Hope this helps.
regards Paul