Aluminum bases are interchangeable....except that there is a dowel pin through the aluminum base into the steel floor base. This pin is installed during final assembly and the location is different on each machine. When you purchase an aluminum base from another machine the hole for the dowel pin will not line up, and it will interfere with installation of the aluminum base. However, you can remove the dowel pin in the steel base and then you can install the aluminum base. For good measure, you should drill and ream an new hole for a dowel pin in a different location....but you don't have to. Phelps machines do not have dowel pins.
When installing the new aluminum base you should do so with the tool head on the machine in the down position so you can line up the powder slide cam in the center of the slot in the powder slide housing.
If you can't come up with a used aluminum base, I have new ones. I can also do the installation on your machine.
Bruce Williams
Star Machine Works.
PS I have never noticed a difference in case feeder cams for a Universal vs a Progressive. Primer slide cams for Universals and Progressives are NOT the same.