The folder "Plug-In Settings“ which you already know from OS 9 versions of Logic. The folder "Sampler Instruments" will be created automatically after the first launch, if it does not exist already. You might want to copy these folders from your existing OS 9 installation of Logic into the OS X installation at the above mentioned location. (Instead of a copy you can also create an Alias).

In case of your "Sampler Instruments“ folder, this makes sure that you can use your existing EXS24 library. Of course, you have to make sure that the hard disk (partition/folder) with the associated samples is also connected to your system. There is no problem in using it from both versions of Logic, OS 9 or OS X.

In case of your "Plug-In settings“ folder you might want to replace just the content, not the complete folder. This makes sure that default settings for new plug-ins like the EVB3, which might not be in an older OS 9 installation of Logic, will remain in the "Plug-In Settings“ folder of your OS X installation. If in doubt, just copy the folders of the plug-ins whose settings you like to keep.

You might also want to copy your existing Autoload song to your Logic X installation. Please remember to save it over, after Logic X automatically converted the "Device“ parameter (ASIO, EASI or whatever you used) of your audio objects to Core Audio after the first start.