This morning I was intent on figuring out how to get the newer version of Logic to not just know, but properly map the legacy sample sounds. It took me a couple of hours and 3 cups of strong coffee, and I found the key. There are also the EXS patches that were in a different location. Once I found the folder for the Legacy EXS sounds and copied them to the newer computer, Sampler now sees Legacy patches and they load and map just like the ole' iMac.
So do the following at your own risk. I have no idea if any weird things might happen by using older EXS files, but it has worked well so far.
Here is what to do. On the older computer, or a time machine backup, go to Computer>Library>Application Support>Logic>EXS Factory Samples and copy the "10 Legacy Instruments" to the same location on your new computer.
Then on the older/ time machine backup, go to Computer>Library>Application Support>Logic>Sampler Instruments and copy the "12 Legacy Instruments" folder to the newer computer at the same location.
Restart computer, Launch Logic and create a Sampler (Multi Sample) and use the menu to load all the missing juicy legacy samples.