So I dropped the magnum in a 65 b-body. I plan on using efi, but started on a different route. Have not finished yet. yours may be a cheaper way or easier I don't know. I used my car as a test car for Painless who was going efi it with their computer. but they canceled the project. I don't have the money right now to buy the rest of the parts to finish it so it stays in my garage.
However I think I can help with a few of your issues.

First, yes the van power steering bracket is different then the truck one.
It will allow it to fit with the battery. It is tight in an early b, so it should be better for your e-body.

There are the two pumps.

Here is the van pump on the motor in the car.


with the battery installed


Here is the air cleaner I picked. with a double stack of gaskets it clears everything.


I got the old 727 to work and gas pedal with some mods to the new cables. So all the regular throttle body and cable kick down that came with the truck motor worked.

Hoses were the worst part. Here is the hose I finally got to work. Comes off a GMC pickup. I have the info somewhere if you still needed.

I tried a bunch of different ones. Some might work depending on which air cleaner you settle on, and if you keep a/c or not.

I used the truck exhaust manifolds.
You can see how tight it is here.




If you got everything then you should have a couple of these parts on the transmission so you can use the truck kickdown cables.


Then I modded the end of the throttle cable for the truck to match up to my cable.




It is all in but the painless stuff and the wide band o2 sensor for tuning.