Sylvanias 4x6 complete HID is a an entry to 4x6 HID, but probably not an option if u want world class quality. I would say that a Narva 80/100W halogen in a quality 4x6 Halogen fixture is better choice.
Others on the board here have ventured the HID route with el cheapos plastic 4x6 fictures with clear lenses that they have done a HID projector retro on as described as alternative 4 on this page:
http://faq.auto.light.tripod.com/hid-upgrade-routes.htm
I was looking into alot of 4x6 fixtures as well before I pioneered into the Hella 90mm units. My SHO almost got 4x6 lamps on them. That would have been quite a retro look!
Anyways, among the ECE units, qualitywise, I found that Marchal units was the best, followed by Hellas and Bosch. (The company Marchal was taken over by Cibie). I have no idea about the stock of Marchal units on a world basis, if there are any left?? I have one unit that I bought for testing for way too much money. Give me an offer if u are interested. I probably have some pics of this unit as well if interested. let me know.