Internal or External Balance?

I checked last night and I have the one on the right middle row for ext balanced 360. So, with that said then I'm pretty certain I have the correct flywheel but I suppose it still might not be properely balanced though the product description said for externally balanced 360's. My next step is to pull the inspection cover off and make sure the pressure plate bolts are still tight. Any more thoughts as to what could be causing the vibration