You are making more sense now.
I think a built 400 would be an awesome engine for a Mustang but the engine mounts are like the 460 and you have to run the large C6 tranny.
It just is not practical.

You need 289/302 engine mounts and matching frame brackets and your engine will sit right in there.
You will need new coil springs and other suspension stuff, too much to list here and now.

Get the engine mounts first.

 

i know i need the motor mounts but other than that and the frame rail mounts...
will the c4 bolt to the 302? do i just need to bolt up the engine and thats it?

 

The 302 version of the C4 has a different bellhousing, so the inline six version will not bolt up. Unless it was a 250.

Don't be discouraged. All of your issues can be addressed one at a time

 

do they make an adapter for the bellhousing? what do i need to bolt the engine to the trans i think this is my only real issue with putting in the engine.
other wise everything else sohuld be able to be used for the time being... as far as i know