I have a 04 viper and want to put a 3 inch riser on just wondering if it will work without haveing to change the brake line.

Usually 2 inches is fine. Beyond that you might need to extend the throttle and brake cables.
You could get the adjustable Rox Riser and find the sweet spot.

http://www.roxspeedfx.com/cgi-bin/cart/showitems.cgi?subcat_id=289