Haven't heard of speed daddy but probably similar to Champion. If it fits a 73 charger like it claims, it will fit your Challenger. However, those Japanese Domestic Market electric fans are totally inadequate for your car. If you want to go electric fans, you need a quality fan/shroud that moves a lot of air. And if you haven't already, you will need to upgrade your wiring and probably need to bump up the alt to be able to feed the fan(s)
I've heard the chevy HHR cooling fan is decent. I prefer a clutch fan. IMO, more reliable, less hassle.
Hope I don't get banned for using the c word there