Saleen also puts UD pulleys. a larger TB, air intake, racecraft suspension and a tune.
I don't think you would be a full second slower, maybe 3 to 5 tenths, and that just depends on how your driving style is and how well you can shift. With a good RT and a 60 ft time I bet you can consistently hit 12.5
2007 Saleen S281 3-valve #170