Big block motor mount question

[402Bowtie]

I have a 396 big block that I want to put in to my '72 k20. Do I need the crossmember from the big block truck or will the crossmember from the 4wd truck work? Depending on which crossmember is used, do I use big block mounts or small block mounts? If it makes a difference, consideration must also be given to the fact that it seems like header clearance problems are often an issue with bb engines in 4wd's. Thanks...John