Sal,
Yep, most of the power is in the heads and cam. A nice ported aftermarket head is light years ahead of a stock FE head.
I don't see anybody offering a template for trimming the Lakewood scattershield, but you can either order an already-modified scattershield from us, or find pics on the web of where to remove material.
Chris Weisberg
Carroll Shelby Enterprises
(310) 538-2914