Well I went through this conversion a year or so ago.
I have a 1970 Challenger originally with a 318 and 904 transmission. I also had a 440 and its mating 727 transmission from a 1971 Imperial that I pulled 30 years ago.
I had a shop do the machine work to the 440 and I reassembled it in my basement. I installed a slightly more aggressive camshaft to mimic the HP 440 and installed flat top forged pistons (since the engine was bored .030 over) to increase compression.
I discovered that my Challenger, even though the 318 was matching numbers, somehow had a B body K member (tried to install stock sway bar and the LCA tabs were in the wrong place and the bar could not go through the K member). I purchased an E body K member and LCAs to install during the swap.
I pulled the 318/904 and driveshaft. Cleaned the engine compartment. I had a couple of rust spots that needed repair and had the compartment repainted professionally.
I wanted a stock like swap, so everything I did would look original and it would reduce the issues with the swap. I went with stock HP manifolds on the 440. This made the engine fit properly and would allow me to install a stock like dual exhaust from Accurate. The smaller Imperial exhaust manifolds will not fit in the Challenger engine compartment! I had to drill holes under the rear seatback to add a bolt on hangar for the driver side exhaust and had to drill holes in the trunk floor pan for the rear driver side hangar.
The Imperial engine motor mounts worked perfectly mounting the 440 to the E body K member. Since the 440/727 is a different length than the 318/904, I needed a shorter length driveshaft. The shorter driveshaft took the heavier U joints, but the yoke on the differential was of the lighter U joints. There is a U Joint that will make this conversion. So the front joint is the heavy duty on all 4 pivot points and the rear U joint is heavy duty on 2 and light duty on 2. Some day I will upgrade the differential yoke to the heavy duty and put in a standard U joint (not the dual size). Probably do this when I go sure grip.
The accessories on the engine were alternator, AC compressor, power steering pump, water pump. I needed only to acquire the alternator brackets for Challenger configuration. The Challenger alternator sits lower so that the belts clear the upper radiator hose. The power steering pump needed no changes. I plan to add AC to the car at some point, so the AC compressor remains with the dual belt setup with the alternator. Separate belt for the water pump and idler pulley and separate belt for the power steering pump. The Imperial had a 4 belt crank pulley.
I installed the larger 26 inch radiator with fan shroud. I did not cut out and replace the passenger side radiator support for the larger radiator, I fashioned a plate that mounted the larger radiator to the smaller opening (I think cooling is sufficient). The radiator upper hose for the 440 connects to the passenger side and lower hose connects to the driver side, so this is opposite the 318 radiator hose connections.
I went with a stock Carter AVS 4 barrel carb and a dual snorkel air cleaner. I replace the throttle cable with one for the 440. I do not have electronic ignition, kept stock distributor with points.
I had to extend the temperature sensor and tachometer wires to reach the front of the engine (my Challenger was originally equipped with the RT gauge cluster).
I added the front sway bar and changed the torsion bars to the size required by 440 Challengers. I still have my front drum brakes, but this will probably be upgraded to disk in the future.
I did this whole job in my garage by myself with my decent tool set, except for the engine installation (I also have an engine hoist). I had a neighbor assist with that.
If you have any questions, feel free to ask.
Jim
