Also, those 9 mm bolts in the flange are hardened shoulder bolts. If you can, use the 74's drive shaft too. It mates well with the tx yoke, and the early rubber center support works fine, though replacing the older one with the sturdier 74 isn't too hard a fit.
GTV and Duetto will have different length driveshafts, but a driveshaft from a 2000 Spider should be fine.
Or, just use 8mm bolts and crank them down (taking up the slack in the forward direction), which some people do, or drill the 8mm holes in the rear driveshaft piece out to 9mm. That is more a common and permanent solution if you don't ever plan to got back to a non-2000 diff.