Who is offering this kit?? I currently have a MK1a in my shop with such a modification, but I suspect it to be decades old. The kit used Nissan 200SX or Maxima vented rotors and spacers between the OE Girling 16P calipers. the dust shields have to be removed due to the increased width of the calipers. As the Nissan rotors are getting hard to find, it’d be nice to have an alternative.
There is no issue with installing spacers… Girling did it themselves with the calipers for the Aston Martin DB5 and Mercedes 230 SL. (type 17-3) As long as you replace the square cut o-rings there is no problem. In fact, it’s 10 times more difficult to replace seals and pistons w/o separating the caliper halves.
I think the fear is, Girling never published any torque figures for the caliper bolts. A good rule of thumb is 40-45 ft/lbs for the 3/8-24 bolts and 50-55 for the 7/16-20 bolts