Stock Vortecs will just handle .455".
Modified ones with better springs and
the guides cut down to handle somewhat
over .550 can be had from hi po Chevy
dealers like Sallee Chevrolet.
Chev also makes a high perf iron Vortec
sbc head with 200cc or so intake ports (the
production stockers are just 170cc) and
a thicker deck to prevent the cracking
that frequently occurs in stock production
pieces. They also have larger valves, etc.
However, you're talking the same price
as Edelbrock's excellent Vortec alum
heads, which will flow better and are
of course lighter.
For intake you'd definitely want the
Vortec Performer RPM (or Air Gap if
you just drive in only warm weather or
live WAY down South).
Go to the Silvolite / Keith Black pistons
website, they have a compression
calculator that factors in head cc's etc.
You just need to know your piston's
compression height spec.
For some interesting sbc combo's, incl
406s etc, check these pages out
http://ryanscarpage.50megs.com/combos2.html
http://www.sallee-chevrolet.com/Cylinder_Heads/sbcylinderheadspecs.html
http://www.carcraft.com/techarticles/56978/index2.html
http://www.chevyhiperformance.com/techarticles/148_0306_406/ (that one is a real monster)