Edward,

You want the 4.5 lb/ cu. ft. density Last-A-Foam (also known as Clark foam),
except if you need some of the 1" thick stuff for the center spar supports -
that's the 8 lb/cu. ft. stuff.  This is what came with my 320 kit.  I'm sure
ACS has it, I ordered some from Wicks a few years ago.

Or you can start off doing what the rest of us do after about 1500 hours of
building, and just order the prepreg panels from Lancair.

Gary