I would pass on the deal. The biggest improvement you can do for your heads is to replace them with a P&P set from a 99 and up Mustang. The current heads you have (me too) are crappy. You can buy a kit for this from "TheGame" that will include the cams. If you just replaced the cams you have into your current heads, the gains would be minimal. Moreover, if you ever get very hi-perf cams and have an automatic, you will probably have to invest in a high stall speed torque converter.
Save up and consider the headswap as a safe and effective mod for your car. Good luck.