73 dart swinger project

The 904 will do just fine if it's properly rebuilt and a good shift improver kit such as a Trans-go TF-2 kit is installed. If you want overdrive IMO your best bet is the Gear Vendors add on unit. It bolts onto the back of your trans. converting it to an over drive trans. There are several other options but the Gear Vendors is one of the easiest ways to do it and doesn't require any floor pan or crossmember modifications. It's not cheap but then again no overdrive conversion is cheap.