Dual Exaust Possible?

I have a 89 Century 3.3, I've been trying to get some dual exaust installed but it seems that no one will do it, no matter where I go. They always say it can't be done, but I've seen many Centurys and Cutlass Ciera's with duals, so whats the problem. Isn't there a way?

I have 1997 century and I have dual exhaust, everything is possible...