Fitted overdrive trans and need to find a starter motor to fit.

If I remember right, a 42RH is also known as an A500. Your original starter should have bolted right back in the same place. That's strange that it wouldn't! You should look for a starter from a Dodge Dakota that is the same year as your 42RH, or a Dodge B series van of the same vintage. When I want to buy a mini starter at an auto parts store, I ask for one that fits a 92 Dodge B200 van. Hope this helps. If you can, post a pic of where the bellhousing area of your 42RH and maybe someone here can offer suggestions.