I had a 55 Crown Victoria with a 351W in it a couple years ago. It had stock exhaust manifolds so I don't know about headers.
It fit good and looked like it belonged in there.
I didn't do the installation so I don't know what problems you'll run into.
It shouldn't be very difficult if you have a little experience and a good welder.
Untill you have the engine hanging in place you won't know what questions to ask. Even then you should have a book or two to refer to. Not everyone on this site gives good information.
Fabricating motor mounts, trans mount and the driveshaft will be the hardest part.
You could use a Mustang floor shifter but mine was hooked up to the original column shifter.

One thing you will need is a digital camera so you can post pictures when you have a specific problem. It's easy to misunderstand a question without a picture.
AL