I have ford rear calipers which have a weight on them, these have never stuck or rubbed since fitting.
Identical to VW item in every other way, I will try and get the lucas number....
Remember that just sticking on bigger discs and pads does not increase breaking performance in all area's
You may take longer to heat up the disc and pads but you lose out on contact pressure, master cylinder upgrade and balanced hydraulic lines are a must to get better braking out of a bigger set up.
I would go for new 288 calipers, good pads and some ATE grooved discs, more than enough for a Mk3.