I think you'll find depending on the motorfactor you will get o/e stuff not on everything though, so like for example clutches luk box the o/e if they don't make it o/e they buy it in. Or a coil o/e on 16v is sagem and if you buy valeo it will the sagem inside.
I work for a motorfactor so tend to know these things lol
There's loads of different makes that box the o/e stuff. Braking is another good one, Bosch and Delphi brake discs and pads are all the o/e ones in the box if they don't make them o/e they buy them in, all other makes I.e mintex pagid textar and ferodo all only do aftermarket stuff unles they make it o/e which I know ferodo only do a hand full of vehicles and so do textar, mintex have the odd car that they make o/e stuff for, but pagid don't make any o/eproducts for any vehicle they are all aftermarket replacements.
Slightly off topic there but just gives you an idea, as for cambelt kit as long as you stick with a decent brand you will be fine S they will be very good o/e equivalents if they arnt o/e ones to look for are skf, gates, dayco, ina are all good ones mate an will save a few quid over o/e stuff
Hope that helps mate