There is no clock option because it is added by default. If you don't make any changes when you run PRSCustomizer, that (the clock) is all that will be added/changed.
So, if you only want the clock, just run PRSCustomizer and immediately click the customize button (although you may need to select the proper firmware version first).
I would highly recommend adding contact information, and checking unified font sizes also.
Any cheap SD or memory stick pro duo card should do the trick. Doesn't have to be brand spanking new.