Trying to figure out what spark plugs I should run with my new motor..

Specs:

350 4-Bolt Main .030 over
Scat 400 Crank
Stock 350 Rods
.030 over Pistons
COMP Cams Hydraulic Flat Tappet (.480 int/.480 exh 290/290 duration )
CNC-Motorsports Roller Tip Self-Aligning Rockers
Stock 350 Heads (1.94 Intake Valves/1.50 Exhaust)
Professional Products Crosswind Air Gap Intake
Holly 650 Street Avenger Carb

Can anyone help me out? Let me know if you need to know anything else.. I think I almost covered it.

 

Most of that doesn't matter, but the compression and type of heads does matter. You didn't say what year heads, or better yet what casting number?
If they are typical stock Chevy iron heads around 1989-ish, then you
will run this size plug:
14mm thread
11.6mm (0.460") reach
with a tapered seat.

In that case I would start out with an Autolite 24
for break-in and initial tuning.

For WOT tuning and full 1/4 mile passes on the motor I would switch to
Autolite 144

For a power-adder that gives less than a 25% power increase, I would use an Autolite AR12.

If you are going to be using a power-adder that gives over a 25% power increase, then you might want to consider switching to Autolite AR135 plugs.

For long-reach or gasket-seat plugs the part numbers will all be different from what I listed above.

 

They are as you described, a stock iron 350 head.. I'll try and pull casting numbers tomorrow. Compression ratio should be between 9:1 to 9.5:1..

There won't be any power adders on this motor and it will only be very occasionally used for 1/4 mile passes. Thanks for the help.