Modern Vespa

I have to replace my aluminum head gasket but I don't want to buy a complete gasket kit if I don't have to. Can I get away with just replacing the head and valve cover gasket or are there others I need to change once I get the head off?

There is a cylinder gasket kit from Piaggio. It's part 497531, and it's got just what you need if you do just the top end. But so does a big bore kit.
You don't need to replace the base gasket if you do just the head, and not the cylinder.

I see there are two different kinds of top end kits for the GT200. One is for cast iron and the other is for aluminum. I'm guessing that all GT200 stock barrels are cast iron and and most kits are aluminum or in some point in time did the factory put out a stock aluminum top end?

Stock is cast iron, kits are aluminum. The extra displacement of the kits is really meaningless if you have a 200. They were more targeted to the 125.

I always use the GTS250 headgasket instead of the GT200. It's thinner giving better compression but needs careful measurement to assure everything has the right clearance.

This will be my first time taking apart the top end on one of these things, so I think I'll just go with the 200 gasket. My only problem now is I can't seem to find a GT200 kit that only has the top end stuff in it. Scooter West sells a gasket set, but I think it's GT250 and that's probably the thinner one you were talking about. http://www.scooterwest.com/items/?_pageCCS=t#page=/item_details/Top-End-Gasket-Kit-Vespa-GTS-250-%28Quasar-Engine%29/9446

Usually pretty easy to just give Scooterwest a call. They know everything and will get you what you need. Often with some helpful advice too.

most GT200 barrels are cast iron, there are a few alum ones floating around but it's rare-- and generally only found on BV200's...

truth be told, if everything else looks okay, just snap a head gasket it on and call it a day. go for the 250 gasket, the chances that you'll have a problem are slim and none (i've done a bunch and have yet to encounter any).

if you want a complete gasket kit motorsport sells one with everything down to the valve seals and stud o-rings for about 65bux

best,
-greasy