Will my slant six starter work on my 440 powered Charger?

Be really careful buying those mini starters. We've started seeing some that will not engage our old Mopars. The one in the picture above looks like one too. See how the gear teeth stop before the end of the gear body? They also don't "throw out" the gear all the way to the inside of the starter nose. Those two things coupled together, are adding up to the starter just spinning and not engaging the ring gear on some of out older Mopars, so pay attention.

But yes, your slant 6 starter will bolt right on and work fine, as long as it was working to begin with.