I'm a windsurfer looking for my first cat. I want to be able to sail with a non-windsurfing wife. I have the chance to get a G-cat inexpensively.
I don't know anything about the reliability of the company, parts availability, etc...
I live in South Dakota. Should I buy it? 1981 5.0.
Thanks for any info.
The parts can be ordered from several sources over the internet. Nice first cat! 
G-cats are nice, sturdy boats and they are great for non-sailors because they have a really open tramp and a forward tramp! I have only seen a few and I've owned one for a short while, but I was impressed.
There are two versions--one is a rental boat with a shorter mast and the other is a standard G-cat. If you get the rental version, you may not be happy with it, but it would be about impossible to get a used stock G-cat mast. However, I replaced my 5.0 mast with a Nacra 5.2 mast. I had to move the tang and all connectors, but it was almost the same size extrusion. The mast base even fit in!
The boat has enough hull to it, that it is screaming for a spinnaker or Hooter sail!
He's looking at a 5.0 mast, which should be identical to a H16 mast with the G-Cat mast-step base. My G-Cat 5.7M mast is a H16 extrusion that is (obviously) longer and has spreaders added.
I believe the mast and rear crossbeams are the same extrusion, while the forward crossbeam is a H14 mast section. There are no complicated systems on the boat, and if the rudders fail you and you cannot repair the (absolutely wonderfully designed) system a H16 or TheMightyHobie18 system can be retrofitted. Vector Marine will be producing a G-Cat F16 in the near future, though I doubt it will have much in common with it's predecessors beyond hull design.