After much trawling through compatibility information and comparing numbers to identify any patterns, and with the valued assistance of the Club GTI forum, i have come to a decision. GT front springs are 871 411 105/951 1xYW, 1xBN paint dots. These are basically unavailable from most brands, though some retailers are listing springs for the GT from manufacturers that i thought to be out of stock. Part nr. 861411105J/952 seems to be the part number that has superseded the above, and checks out fairly consistently in compatibility information, so i think these fit a GT. Part nr. 861411105J has sketchy and inconsistent fitment details for the GT, but patterns begun to emerge in cross referenced part compatibility information, and i think these will go on a GT. I've placed an order on Autodoc for a pair of 105J/952 by Lesjofors, and a pair of 105J by Bilstein (these are the B3), so i can place them side by side and see if there is any difference at all. I can also measure the coil diameters with the verniers. None of the above part numbers are available from VW classic parts. It's been quite a challenge to establish exactly what it is that retailers are offering, and i suspect that the buyers at various retailers have little idea exactly what OEM part numbers correspond correctly to their product.