Replacement light fittings set into a "shelf"

We have a sort of shelf above the window in the kitchen with 2 light fittings set into it. They have been there about 20 years, and recently when I was replacing a lamp in one, it fell to bits. I can't see me managing to get a replacement, so I was going to replace both of them. However, they sit in holes 4.5 inches in diameter cut through the shelf, and I can't find anything that might fit, as all the fittings I've looked at are much smaller.

Before I start modifying the shelf, any idea wher I can find a couple of fittings for 4.5 inch holes?

is this any use? http://www.tlc-direct.co.uk/Main_In...ghts_Index/Downlight_Converter_Kit/index.html

That looks as if it is just what I need without faffing about with the shelf!

Many thanks for that.