Unless you just want to have lights "for looks", save your 60 bucks for something else. I think I paid around 60-70 bucks for the conversion kits. Each kit did two lights, so I got 3 kits. The two lights on my bumper are Hella 700FF's.
I know you may not have the cash for better lights, but seriously, dont buy those things. I had people tell me the same thing before I bought mine, and I wish I had listened. If you dont believe me, send me 10 bucks for shipping and I will send you the extra two cheap lights I have for free. I only used 6 of the 8 that I bought, and the other two are still in the box, never hooked up. Then, you can at least see for yourself they arent worth any price. Your 500's can be converted to HID very simply, and you will have VERY good output. The 500's are the minimum quality light I would buy, and I still would convert them to HID. Once you use an HID auxillary light, you will NEVER go back to a conventional halogen lamp, I promise you that. Your two Hella 500 lights, converted to HID, will put FAR more light than 8 of those cheap lights, and you will only pull a fraction of the power. 4 130 watt halogen bulbs pull a LOT of amps.