EFI Magnum engine/trans in old A-body (65 Barracuda).

check out this thread.
5.9 Magnum into a 73Duster , by Old Geezzer.
I think the new Hemi may be too wide for the early A body, It barely fits in the late A's.
"Maybe", if you go rack steering it'l fit.
For the 5.2 or 5.9, I would look at the Spitfire headers. The magnum heads have the same bolt pattern and ports are similar.
Floor and torsion bar xmember mods for an OD trans will be significant but doable.
Shortened driveshaft for sure if OD used.
Many fuel pumps, and fuel regulators to choose from.