Internal or External Balance?

The reason for my question is I just finished having the 4-speed rebuilt and put together with new clutch/bearing/flywheel and now there is a slight vibration at 2krpm and above. And everything appears tight and i was wondering if i had the wrong flywheel. The one I put in has three large holes on the engine side which is for the ext. balance 360 but the one I had removed did not have the 3 holes.