G'day all,
I'd go with nath here. This 'stack pulley' is a design that will get rust-bound if any moisture at all gets in between the pulley sleeve and the shaft.
Since it's now knackered anyway, I'd have at it with a thin cutting disc on an angle grinder.
First cut a wedge out of each of the pulley sheaves, to allow you access to run a lengthwise cut all the way down the tubular sleeve. Don't worry about marking the shaft; it won't cause significant damage to it.
A bit of prying at the cut edges will loosen things up enough to get it off, with the aid of a bit of CRC, Inox, Penetrene or similar penetrating lube.
