Friend is swapping his straight six/4 speed/205 to a 460/C6/205 on his 80 Ford.
Now we have a few questions, are we going to need a new engine crossmember?
And as far as motor mounts can we just change the plates and get big block mounts? Are the clamshells the same? Thanks in advance

You need 460 frame mounts for a 80- 97 ,and motor mounts for the same. The pass side bolts in and driver has 1 or 2 rivets and bolts

So the plates on the crossmember that the frame half of the mount bolt to will work?

No, you need 460 stuff for both sides. The straight six stuff doesn't interchange with any V8.