Great initial post after 9-10 months of being a member with a real honest question!
What your told is totally up to you, with who says what with there experience in mind! Basic is, your'll learn who is a chimp that poops in hand that throws it outside of their cage fast.
Okay back to your question assuming the air range(r) is a real air ranger hull and worth a retro fit from 1996 build?
First off before any motor or redrive choice is why skeptics say it's not worth it?
Granted new hulls are built daily to those that have tweeked an old or new one? Junk is for sale everywhere, even out of the box junk!
Back to your question,
Prop is sold for whatever you can get going gear or belt! That prop is now useless to you going reduction drive unless you go belt with thoughts of matching it with more blades and a hub, which should involve the prop builder! 72 on a 16 foot boat is like a garage sell build or maybe a real cheap cad build!
You can do 72 on 16 footer as a water only boat if that's the goal? Many on here do?
You would be better off asking air ranger if your hull is worth rebuilding at this point if your lost to the hull needs or power requirements!
Okay back to your main question! Most redrive uprights are 12-13 inches forward of the transom at stringer or tbar height and all shifts forward.
Only you know if your dd air ranger hull and cage could work for what your asking. If me, I'd junk the 1996 motor stand for good measure?