You need to hold the slide back against spring pressure to remove the slide stop. There is probably a small hole drilled through the guide rod so that you can put a paper clip through to hold the spring compressed while removing the guide rod (which also makes reassembly much easier). Anyway, that's the normal procedure with a bull-barrel. The same procedure can be used to take down any 1911. If you've ever seen Jackie Chan do the one-handed-field-strip, it's basically the same thing.
Wish I could buy that gun in CA.