73 Duster

A 351 Cleveland is another option, but the Windsor is a more common motor, produced until 1996, I'd think a 429/460 would be a fairly tight fit, and can be pretty costly to build. 390/428 would be harder to find, and likely very expensive to build. The 351W was available in the 69 Torino/Fairlane line in 1969, another reason I would give serious consideration that motor.
Eh one of the mods will fix it, not like there's Ford small block into a Duster sub-forum.

Just don't trivialize the fabrication work that will have to be done. It all seems pretty easy until the transmission hits the tunnel, the drivetrain angle is wrong and the torsion bars hit the pipes. And no one has a solution because you're the first one to do it. Also, if you're used to other musclecar platforms remember that with the torsion bar suspension the transmission crossmember isn't just along for the ride, that upper crossmember section carries all the suspension load too. So you have to do a good job, not just take a hot wrench to it until it clears and call it good. That's a great way to turn your car into a pretzel with torsion bars.

There are a couple of pretty detailed threads on swapping in a 200r4, I would wager the Ford AOD swap would be similar. Just food for thought. US Cartool makes that crossmember too.

Will GM 200r4 work with factory floor shift location?

I'm not saying don't do it, but you can get running 318's for darn near nothing. Same for small block 904's. Heck I've got a small block 904 that I ran around for awhile, shifts decent and has a deep pan on it. Couldn't sell it for $100 at the swap meets. For the kind of time it will take to do the swap right, you can probably find a decent running 318/904 combo for less time and money.
You disagreed with me but no explanation? I wonder why they're so similar?.. not arguing just learning..