Now, don't take this the wrong way, an 11 second GN is an impressive street car, and having bought a new 87 GN in 87, I know how much work (and by looking at what you've done to it, LOTS of money) was necessary to run that first 11! Having said that you have to look at what cars are currently out there, what they run and the small amount of money needed to get them into the 11's. A new 5.0 Mustang is over 400 HP from the factory, and you can find deals on them for under $30K. They run mid to low 12's on a cool day and a decent track, and a simple $800 or so gets you a NOS system, that puts them into the mid-high 11's, Camero's are basicly the same, and even a Hemi anything with the same NOS system is pushing the 11 sec. zone.
For example here's a stock 2013 5.0 with X-Pipe, tune, and DR's going 11.80's!....all for $1-1.5K!
You buy a new BOSS 302 for around $40K, the new deal here is a Hellion twin turbo system INSTALLED for under $12K and it makes 750+ HP at 9 lbs. of boost, and 835 HP at 12 lbs. For $10-$20K LESS than the 2013 Shelby GT 500, you have as much power as they have after they add on all the bolt on's they use to run 9 second passes.
The GN's are fantastic cars, to pull the power we do out of a DATED V6 is a labor of love. BUT, having said that, there is much faster and in the long run, cheaper ways of doing it on 4 wheels.