Sit down, this is long, but worth it.
1.Super Stealth RamAir Intake, Stage 3 OR see the homemade knockoff version at www.azsupersport.com
and look under 'intake'. This intake flows within 1% of all other cold air and ramair intakes, is safer than other RamAir intakes, has greater potential than other RamAir intakes, and, when you add the Suncoast RamAir hood, outflows the SLP RamAir hood as well. It's a good intake.
2.Throttlebody coolant bypass. Do it.
3.160 degree thermostat. Do it.
4.Water, plus Amsoil RMI-25, Redline WaterWetter, or Nology NotHot. Since you live where the temp will never go below 0 degrees F, H20 PLUS any of the above additives will negate any corrosion caused by water (slightly acidic at higher temps, hard to remove impurities), and will raise your boiling point safely above 250F, while removing heat more effectively than H20/antifreeze mix.
5.TransGo Shift kit. Within it, there are choices. Don't get carried away.
6.If it IS a 9C1, do the Stealth Bolt Brake Bias mod. Your rear discs aren't helping as much as they should, until you do this mod. Less than $100, VERY effective.
7.Rear end-go for 3.73 ring'n'pinion. Don't forget, you need a new ABS driveshaft reluctor. Optional: get a limited slip.
8.Contact Bryan Herta at www.pcmforless.com
once you have completed all these mods. Even though he has only reprogrammed LT1s to date, I think he can help your L99 fully utilize the mods above. Mention to him that you want your AIR pump deactivated, as well as all other mods.
For less than $1000 if you don't do any of the work yourself, you'll feel a difference.
Since you mentioned that you are eventually gonna swap engines, don't do anything to the L99 engine itself.
for other mod ideas.