As far as I know, the Konverter does both... But rest assured, if you got a GT, you are lucky. Not only that it's rare and worth slightly more than the Turbo, There are also more Japanese Games available than T-Grafx games on the second hand and online market.
P.S. Did you notice if it has low sound? That's important to me 'cause all pce's and turbos I have encountered had the problem. Mine is coming next week (turbo express, boxed and new, but with low sound as well)