Maybe it's just the pics, but do they raise the floor of the plenum and then slope it down towards the runners? Kinda like a built in "turtle" for the plenum floor?
Or does it just look like that b/c of the way the machining pattern looks?

CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax