The kit he linked to was developed by my company FTR and is a very high performance yet economical option. Its the same kit that @iroush / BTM Autosport is running on his 99 roush, and we have gotten very good feedback on it.
The configuration is 14" GT500 rotors with s197 calipers, and it does require the use of 18" wheels.
Assuming they are in good, working shape that's not a bad deal - it's a little under half-off if you source them new. An example of new ones would be from LMR (link) and those go for like $600 or so. You also might be able to find Bullitts/Mach 1's floating around online at some not as well-known stores.
If you are trying to fit a 15" wheel in the rear, you are probably better off keeping the stockers in the rear and just upgrading the pad (I think it'll fit a 15" but have not personally done it). The Cobra/Bullitt/Mach 1's in the rear will need a 17" wheel (though maybe a 16" might fit, not sure?). 17" min up front for sure with the Cobra/Bullitt/Mach 1s.