1965 Mustang Coupe, should I get an entire new exhaust system or keep the one I have?

I have a 1965 Mustang Coupe and it currently has a 289 V-8 and I think I am going to drive that engine until it dies and the previous owner converted the dual exhaust to one tail-pipe and welded a flow master muffler. It sounds great and I like the deep powerful rumble that it makes. But when I raise enough money I want to replace the 289 with a 347 Stroker and I want to have that deep powerful rumble and have a nice clean but strong idle