Can I fit a split-back dual exhaust onto a 1989 Pontiac Firebird Base Coupe

[BK_FAN#12]

(2.8l V6)? Here's the one I was looking at-

http://www.flowmastermufflers.com/searchfmm/search_cat.php?cat=2&sub=21&sc1=&sc2=&sc3=&sc4=Dual%20Rear/Side%20Exit%20DOR/DOS

..... and if so, how much HP will it add?