I think you will find that both of these jobs are easiest when the mast is unstepped, so I'd do them over the Winter before stepping the mast next Spring. I'm confused about your comment "unable to step mast", because you really are best to do the work while the mast is unstepped for the Winter, that way there is no tension on the rigging and while installing the furler you won't need to hoist anyone up the mast to take measurements. Replacing the masthead sheaves is easier with the mast unstepped since you can more easily pull the halyards away from the sheaves while doing so, if done with the mast stepped you have gravity working against you, plus again, the need to hoist someone up the mast to do the work. With the mast unstepped, if you drop a tool or one of the sheaves (or worse the axel pin) it will fall a lot farther and who knows where it may land, with the mast unstepped it falls to the ground right under where you are working, maybe 2-3'. A lot easier to find it. As I say, as long as your mast is unstepped, now is the time to do it, I agree, I would not want to step the mast before this is done, do it while the mast is unstepped.
