Congratulations on your new old Hobie! Your rudder is not compatible with the T&S system, but should work fine for you. For best performance, make sure to pull any slack out of the (centered) rudder lines and adjust the center rudder position so it deflects the same in both directions. Don't worry about centering up the handle. Adjustments are easily made at the rudder.
Is there a problem with your seat? I prefer the older style back combined with the i-comfort bottom. You have to do a little custom modification to get it to fit, but it's not difficult. Or you can get the newest seat and adapt it to your old style seat plugs for a direct replacement.
Contact your nearest dealer for any parts.