Exhaust System on Stock 273

I currently have a stock 273 in a '68 Dart. I'd like to possibly squeeze some more power out of it. I've currently got what I believe is the stock system where the exhaust crosses over underneath the bellhousing and connects to become a single exhaust with some aftermarket muffler welded near the back. I've also noticed that right past the driver side manifold, there is a decent sized dimple knocked into it.

I was wondering what the going rate of having an exhaust/muffler shop installing a dual exhaust system on from the manifolds back? It doesn't need to be an H or X pipe system as I want to do this on the cheap. So that means no headers as I have power steering as well. I was thinking of just getting 2.25 or 2.5" straight pipes back and dumping right in front of the rear wheels or out the back. I was also thinking about providing Dynomax Super Turbo mufflers too. What are your thoughts on this?

Thanks for your help!