Stieg should have a serial number stamped on the blower, call them and find out what stage the blower is. I would guess if it's a 3 or higher, your already around 500RWHP
I would also guess that the stock inlet and T/B is ported by Stieg.
Then again, if you don't have a BAP or Injectors it might be a older port making less HP.
Shorty headers are a WASTE. The stock manifolds are actually not to bad, and have suppourted over 600 RWHP on many 03-04 Cobra's With a ported Eaton set up IMO even long tubes provide marginal gains and are not worth the cost of install.
Do you have a IRS brace? I have a Billetflow for sale if needed. (Shameless plug)
Full length subframe connectors are a good idea.
Gears? Eh, I would not go any steeper than 3.73 IMO, if you have the Diff out, IRS brace and get some good Diff bushings, Like MM alum one or Burces kit from SVTP.
There is also another Dyno shop in the area in Lathem, C&C Motorsports, I could get you the phone number if interested.