I'm ready to buy a flex-plate for my BB. They come with two different number of teeth. My starter has nine teeth on the gear, which flex-plate do I need with this starter? Thanks.

BB will use a 14" 168 tooth flexplate, which is used with a starter that has a nose mounted with offset bolts. Smaller 12" 153 tooth flexplate is normally used on 6cyl and 307s and uses the starter nose with inline mounting bolts. Starter pinion tooth count is the same for both. If you have a 454 make sure you get a 454 flexplate, 454s are externally balanced. Try a search for more info.