Launchbox lets you choose your cores. You just go into Manage Emulators, then go to Retroarch and edit. This will bring up window and go to the middle tab which is Associated Platforms and there you can set the exact core you wish to use. For example the Super Nintendo platform for me has:
-L "cores\bsnes_mercury_accuracy_libretro.dll"
If you want to use a different core, just make sure you have the core you want downloaded in your Retroarch/cores folder and change the line accordingly.
I wouldn't wait til 1.3.7 either, now is a good a time as any to jump in and get it all set up.