They flow just fine at high rpm's lol. I pull my 355 to 6500rpm. It made power all the way to 6750 on the dyno never really falling off. That was through extreamly restrictive exhaust too.
The 170cc runners will support your 406 just fine to 5400rpm depending on cam selection.
Wont take much cam, try to stay under .500 lift. Vortecs flow best at .450-.500 and start to get turbulent above that.
Something like 210-215* intake and 220-225* exhaust duration. staying right around .500 lift on each. Keep a little wider lobe seperation, the fast burn style chambers like the cylinder pressure. I run 10.2:1 on pump gas.
__________________ 02 gmc rcsb, 3/2 lift, 4.8L, auto,3.73's,airaid jr, lt's, magnaflow tune, 212/218... 295/288 rwhp/tq
70 Nova (Barney)All iron NA 355 ..firstname.lastname@example.org 1.70 60ft.
04 gsxr .6L back to a 600 lol