Agree with Jphii, though having the armtube *approximately* level for an "average" thickness record (whatever that is) is not a bad idea. I agree it's not worth fretting over though, the cartridge-record relationship is far more critical than the armtube-record relationship.
I haven't heard that a 103 is shorter than a normal cartridge, but if it is you could always add a headshell shim.
I haven't heard that a 103 is shorter than a normal cartridge, but if it is you could always add a headshell shim.