Starter for 8BA Flathead with Merc-o-matic

[Detroit Flathead]

I recently learned that a 1951 Mercomatic / Fordomatic starter has different mounting with a tab for a bolt sticking out from main body, a different drive assembly, and different toothcount. I'm mounting this to an 8BA Flathead. I need some help determining if either of the starters pictured below are for an 8BA with a Merc-o-matic. I've been told the one on the left is, with the tabs on it, but it doesn't seem to mount correctly. Can anyone else throw in their two cents? The starter on the left with tabs has 9 teeth. The other starter, with the corkscrew shaft, has 10 teeth. Does anyone have a picture of their Flathead with automatic transmission and starter installed? If these aren't for an automatic, do you have one for sale?

If this looks familiar, it's because I also posted in on Jalopy Journal a week or two back. Perhaps I can get more info here. Thanks.