Thanks again guys.
Some issues--

The existing fixtures are 480-volt and connected to a 3-pole CB.
There is no neutral available, so they need to stay @480. There is a short somewhere so the whole bank of lights (20 fixtures) is out.
I'm looking to install fused fixtures, so I need to change the whole fixture.
I dont think fluorescent fixtures are available at 480-volt? And to keep retro-fit costs down, I'm looking to use the existing stem (nipple) mounting.