Originally Posted by Stumble
That is one seriously old school system. For what it's worth I would go to an internal cascade system with a clew strap. But there are a number of places to get those sheaves. Zephyrwerks - The Sheave Factory
custom makes them for about $30 a pop, or you can try to size match with either harken, Schaefer, or Lewmar. You may have a problem finding wire sheaves these days however since wire rope is becoming increasingly rare.
The funny thing is, the "old school system" doesn't appear to be the first! As I started disassembling the outhaul I discovered a hole in the top of the boom and can see a internal sheave!
But then, I now recall this boom was originally one that Furled the main, so who knows what went on. The trick now is to remove the end cap to see whats going on, and possibly do an internal system. They used slotted stainless screws in aluminum that (of course) no longer want to come out.
The other option (if a internal system is impractical), is to restore the old school system. The wire rope was 3/32 or 2 CM diameter. I wonder if there is Spectra or some type synthetic that will do the same job if I can find replacement sheaves. If so, that may be the simplest way to go.