I have a G-tech to check out changes on my car. I know it's not the same as a drag strip time slip but it seems very repeatable & I use it see how changes affect my car.
In my 05 GT (that I no longer have, SAD STORY!) I used it one night & had 3 runs within .05 sec of each other (a best of 13.27 in that modded car!).
Anyway, my car had Delta tires on it & would spin easily. Recently switched to 225 16 BFG Sports. Not the greatest tire but my best ET went from about 15.1 to 14.5 just from the better traction. My 60' was 2.15 & before it was about 2.5 I think.
I have a 93 302 with old Edelbrock F4B & Holley 570. No headers, stock but new suspension & I think 3.4 gears. Door tag says they should be 3.0 but checking them seems to be 3.4 ratio.
I have C-4 auto with shift kit & was manually shifting at about 5500 RPMs.
Long story short, tires knocked over half a second off my ET.
Now I need heads & headers & I be flirting with the 13's.

Best way to spend the money to go faster with that car is on a good set of drag tires. You can find them on craig's list cheap. Next would be on a gear set and a posi. Keep the 8 inch, it will do fine. Loose the air shocks. Spend a $1000 and I will bet you will be in the high 14's.