Header flow numbers

Here what I have,

84 LA Block, Bored to 4.030/forged crank, rods and pistons (4 inch stroke) 408 ci.

RHS LA-X Heads, valve dia. 2.055 intake x 1.625 exhaust
60 cc Chambers.
These heads flow to 270cfm

Cam, Bullet Hyd. Roller
Duration at .006, .303 intake, 315 Exhaust
Gross lift 563/563
108 degree lobe separation
1.6 Hugh's roller rockers

Edelbrock Performer RPM Air Gap intake. I haven't decided on a carb just yet but am leaning toward an Edelbrock 800CFM AVS or Performer electric choke.

My question is, how much will the TTI shorty headers effect the performance on this engine combo as far a street cruising (not a daily driver or racer)

I thought this was a big block A-Body header discussion......