The transmission for the 400 will work fine with a 460.  Chances are the
exact same transmission was used behind both engines.
You will need a truck oil pan and oil pickup tube for that truck pan.
You may need different 460 truck motor mounts, they could be the same as the
400's.
Some of your accessories (alternator, air-conditioning compressor etc.) and
their brackets might need some modification.

Your decades old car application engine and water pump may not have outlets
in the same places as your existing radiator and hoses....

Hope this helps, and good luck with your project.