I used the easy way out and installed the JamPacks again by buying MainStage 3. It is a bargain price compared to the price for the original Jam Packs. Installing MainStage 3 will install all five JamPacks: https://discussions.apple.com/message/31642404?ac_cid=tw123456#31642404
MainStage is installing the Sound Library and the Loops in the same directories as GarageBand or Logic. So GarageBand will see them. But not all sounds and loops are compatible with GarageBand. Mainly the JamPacks and compatibility loops and sounds will work, but that plenty of very useful software instrument loops and sounds.
After installing MainStage 3, launch it and use the command "MainStage 3 > Sound Library > Open Sound Library Manager".
When the Manager opens, scroll down to the "Legacy" section and click the disclosure arrow.
select the Jam Packs you want to use. I installed all from the Legacy section.
Click the checkmarks to the left of the JamPack you want and then "Install". The packages are gigantic. You will see the size when you select them. Start with the ones you really want. The download may take a very long time.
After installing the sounds and loops, restart the Mac. Then launch GarageBand and use the command "Loops > Reindex All Loops" from the Loops Browser.