. . . .or, what does it take to build a competitive road track car, starting with a 2005-2010 Mustang GT? . . . and, is it worth it?

I've been doing HPDE's for a few years, and feel like I've hit a wall on my lap times. Well actually, my latest time are about 2 seconds slower than my best from a couple years ago ..... was humbled at the SCCA Time Trials in Thompson last week! I am classed as T3 due to adjustable camber plates, which puts me with more capable cars, such as 2011+ S197's...

can an S197 4.6 be a competitive road track car?