Roof cross bars

hello all
I managed to buy some cross bars which fit inbetween the existing rails (or so I thought) got them cheap went to fit them and no holes. I know I should have checked but they were so cheap.........
anyway they came off a '99td5 (I have a 2000 V8 )but when I have been out and about I have been looking at other roof rails and none have had the holes in. There are some for sale on flea bay off a '97 tdi which have the holes in ........... so I have 3 questions
will D1 roof bars fit a D2?

can I drill the existing rails (the pins are 6.8mm so I guess a 7mm drill bit)?

why do some have holes and others dont , were they a factory fitted option?
thanks in advance
Andy

If this helps I have a 300tdi with factory roof rails and cross bars, my cross bars have the pins and the rails have the holes, my dads got an early TD5 with factory rails so i will check his next time i'm over.

I've got a 93 200tdi with rails and crossbars with holes and pins. Thinking of fitting em to me new disco

On my Td5 the cross bars clamp onto the roof bars.