I have a 2002 Astra 1.7 DTI estate and the gearbox has gone (loads of play in driveshafts, bearings gone, whining noise between 30-40mph and oil leaking). Local garage will fit one for £200. Seen one on ebay, agreed £60 with seller, guy emails me to say will fit my mk4 Astra but I’ll need to swap speedo drive.

Do I need to be more specific to get the right gearbox or are they pretty much generic across models?

As long as it’s coming from a 1.7DTi with the same power output you should be OK.
If it’s from a petrol or a different power output diesel, it will more than likely have different ratios or perhaps even an extra gear (my Ibiza has 6 gears – 1.9TDi with 130 bhp, but the 1.9TDi with 100bhp only has 5 gears)

Not sure about the speedo drive, sorry.

im sure on an 02 astra the speedo picks off the wheel sensor on the passenger side front…