i've been told the stock newer type one piece headlamp will replace the older two piece headlamp(and indicator). is this true? does it matter if i replace valeo with bosch or vice versa? what about the spot lamps in the headlamp unit itself?

 

Yes you can replace the two piece headlights with the one piece ones, but it requires some modification. First the fenders on the older pre 99.9 cars have a lip that must be ground down. Second there will be some rewiring as they use different plugs.

Most people when they do this go for Ecode (european clearcorner lights).

http://www.audiworld.com/tech/ext17.shtml