so my 2 cents:
- rust / crude: just chisel it out to make room to pass teh belt
- pulley: with a metal file, round just the sharp edge of your shaft, and the edge of the pulley where shaft goes it. And with a fine sand paper, make sure everything is smooth. It does not take much at all to make pulley installation difficult, especially when you work "upside down" and "bent backward" as most of us... the "key" could have moved a little when you removed the pulley, and prevent the reverse operation: make sure it is flat, or slightly inclined toward the end of the shaft.
- battery: it is possible, especially if you need just to get in and out of the marina, and you re-charge every night... but I would recommend to get pulley back on first: shaft do not grow in size overnight