I shimmed my tank today. After replacing the stock bolts with ones that were slightly longer it took 5 washers on each mounting bolt, 7mm a side, for a total of 14mm, to take up most of the space. The tank still has some slight movement, but to eliminate all movement I would have had to get longer bolts to add any more washers. (I also worry about loading the tank by putting pressure on the mounts if I add too many washers - after all I suppose the tank can only stretch just so much before something gives somewhere on it). I am now going to monitor the tank carefully to see if it continues to get looser. Pretty amazing that the bike had over a 1/4 inch of extra space on each side of the front mountings. The interesting question is whether the bike originally had this much play and I just did not notice it, or whether it has developed over the 2 plus years and 8,700 miles that I have had the bike.
2007 GT1000 (14 tooth & Ikons)
1964 Norton 650SS (runs good, but marks its spot)
1974 Rickman 750CR (in progress)