If you want to reduce droop by just 0.5mm, do it on the springs. Just wind the nuts up or down a couple of flats until you get what you want. The car doesn't seem that sensitive to such small changes to static camber angle for my driving ability - 0.5mm is not a lot in the grand scheme of things! Watch the ride height when you do that.
The alternative is to slip an 0.5mm washer under the front or rear 'beams' to increase the height of the down stop 0.5mm. If you can get plastic washers, you make a single cut from inside to outside and then clip them over the screw - saves you having all the hassle of taking it all apart just to get a spacer in.
The spacer option is best as it means that your ride-height is unaffected. If you need to change ride height you can clip the washer off, or clip another one on. I have a range of old 12th spacers (actually 0.030" as they are originally imperial thicknesses) that slip over the screws, but don't fall off as there is no side load on them.
Please don't forget that ride height and droop must be checked with the body on because GT12 bodies weigh so much. once you know how much effect the body has on your setting with the rolling chassis, you can allow for that. In my case, I use 3.8mm on the front and 4mm on the rear. When the body is on, both ends are 3.5mm ground clearance. Front droop is therefore 0.8mm to 1mm, and rear about 1mm to 1.5mm with the body off. The difference is because the rear springs on mine (yellow) are much softer than the front springs (red or blue for me). With the body on both ends are between 0.5 and 1mm droop and again, I can't tell any difference on the track.
Play with the droop as it affects weight transfer and you may prefer the car's handling with more weight transfer (more droop) at one or both ends.
I don't do FacelessBook, so if anyone has any questions from there please post them here and I'll answer them. HTH
