my first mopar, will i love it or hate it?

Just picked up a '73 duster 318 automatic. Its a little rough around the edges but it runs strong and the PO put a big brake kit on so it stops on a dime. I've always been a Chevy guy and have spent quite a bit of time in the European import scene but I took this duster on trade and its starting to grow on me. I'd like to get more power out of it and I was thinking of building up the 318 but a buddy of mine said that would be a waste and I should just buy a 340.... Any input there would be appreciated. Also I need to replace the interior, anybody in the south Seattle area with spare parts would be awesome. Anyways, greetings to the mopar community!