The Mk2 Astra digi dash uses a magnetic pickup that bolts onto the standard gearbox drive, in order for it to work in a VW this part - or at least something similar - would need to be retro fitted to the VW gearbox.
As for the other stuff, I'm really not sure. Bear in mind however that the digi dash has a oil pressure guage which would require some kind of aftermarket (or Vauxhall OE) sensor as the Mk2 only had a oil tempreature sensor.
I might be able to find you the part number for the Vauxhall speed sensor, and as it happens I've got a Astra GTE digi dash for sale with 80k on the clock... PM me for the part number or enquiries on the clocks
