Suggestion on New 3rd Member

O.K., I have now less than a month to button everyting up and hand a Firebird his *** at the track. Will anyone give me a suggestion on picking a gear ratio for my new replacement 3rd member? Here is my current combo:

408 Magnum
Stock Eddy Heads
Speed Pro Forged Pistons
Square decked and cylinders honed with plates
Eagle Crank SIR Rods
10.5:1 compression?
Hughes Roller .555 Intake, .565 Exh., 242 and 246 @.050
Crane 1.6 Rockers
Milodon Windage Tray
MSD Ignition
Black Magic Electric Fan
M1 Single Plane
Quick Fuel 750 Q Series
March Underdrive Pulleys
Dynamic 9 1/2 converter, 3700 stall
998 with 2.74 first gear
Currently 3.91 Sure Grip, growling like hell and 235/60 BFG Drag radials that act like your driving on ice when you matt it.
Waiting on 275/60 M/T's to arrive.
What gear, and setup and from where to order?
Please help.
His car
87 Firebird, 350, Dart Heads, 750 Demon
His time so far in 1/8th which is what we'll run: 8.7 @ 83

Thanks Again!