There were a couple guys that did a Hemi transplant on teh Drydock: a green 72 or 73 Fury wagon, an orange 68 Sport Fury fasttop, and a 3rd one that I don't fully remember (maybe it went unfinished?).
As for the Torqueflite - it needs to be a smallblock trans to bolt to a new Hemi, not a bigblock trans.
If doing a trans change, might as well do an OD - either a hydrualically-governed A518 (self-controlled) or the one mated to the Hemi - but that one is electronically-controlled, which usually means a junkyard controller re-flashed to erase the original-VIN stuff. There are some aftermarket controllers for some of the Hemi trans. The truck A545 is more slender and reportedly an easier fit, but IIRC no aftermarket control for that one.
But any of those OD transmissions require some surgery and crossmember fabrication, plus shortened driveshaft.
IIRC there might be an adapter flexplate or something to fill in the gap between TC and crankshaft.
There have been some issues on many different chassis with the old filter setup hitting the crossmember.
I don't know what the oilpan clearance is like with the centerlink and idler arm, but I'd expect some issues there.
As simpler/cheaper method to improve drivability and mpg might be a newer throttle-body type of EFI system, one that includes control of ignition timing.
More complete control of timing can give more torque.
An EFI system can prevent fuel boil-out at the engine, which helps MPG. We lose MPG when we lose fuel.
An EFI system that returns to the fuel tank can lose some benefit by heating the fuel in the tank, and an old-car tank cannot seal/recover the vapors like a modern tank.
A returnless EFI system (I think some of the new ones are this type) modulates the fuel pump to only send the engine what it needs, keeping fuel temperature lower. A return-type is constantly ciruclating fuel from the hot engine fuel rails back to the tank, and it re-circulates the most fuel when fuel usage is *lowest* (which is most of the time).
An EFI system can also be mapped to drop fuel at closed throttle and 1500+ engine rpm. My wideband O2 sensor shows my carb goes really rich under that condition. I presume this is due to the engine RPM causing high vacuum and suckign more fuel than they'd normally do at idle. The carb doesn't really know you're coasting - the EFI does.
If you have an original-spec '66 383, you have small-valve closed-chamber 516 heads, which IMO would be a good choice for high airflow velocity for street driving, and probably better MGP over the later open-chamber heads - a prime candidate for EFI to boost MPG. Just my opinion there, no data to back that up.
