383 + 71 Demon = what parts fit?

No motor plate, this is pretty straightforward swap. See:
http://www.engine-swaps.com/Pages/ArticlePages/GoBig.html

Schumacher mounts are simplest way to go to replace the S6 with a B and are fully sorted out for clearance. Manifolds work but are chokers - I would seriously consider his headers too.
http://www.engine-swaps.com/Pages/ProductsYear/67.72aBody.html