auto gearbox to manual

can anyone tell me what sort of a job it is to change an auto gearbox to manual on a 1988 1.6 cabrio?

Lots of work involved but achievable. You will need manual gearbox with levers, connecting rods etc, clutch cable (kit), pedal box, starter, ring gear off manual flywheel plate or manual flywheel, full clutch itself, GTi steering rack etc etc … and you'll need to do away with the kickdown set-up from your existing set-up.

...gearbox mounts, throttle cable, clutch cable, probably a few other parts too. Most people would sell the auto and buy the manual.