Outdoor Light Fixture

We have a rather large wired pole in a bricked planting bed that is in need of an outdoor light fixture. I have been searching for something that is A) large enough not to look dwarfed by the pole, B) generally matches our existing coach type lamps on the home, and C) has a bulb that is accessible from the side rather than the top.

Finding something that fits all of this for a reasonable price has been a challenge. Recently at a Habitat for Humanity Store I picked up a used fixture that I think might work. The wiring is in good condition, and it has the large mercury or magnum socket. There is a sticker on it that is difficult to read because of the location. It appears to say "4-KV pulse rated".

This is not a fixture that will be used a lot. I know nothing about these sockets or bulbs. If I use this as is, is there a specific bulb to look for, or should I consider replacing the socket with a standard size? Is there an advantage to keeping the current socket over rewiring it and using a CFL bulb?

Any comments at all on this would be appreciated.