Yes, the spark coil studs changed from 5/16 coarse to 3/8 fine in 1955 - regardless of which frame was used ***. My 1954 KH has the 5/16 studs, and the holes in the spark coil are 5/16. I believe this coil is original to the bike. My best guess is that there was an undocumented change (3/8 holes) in the spark coil bracket in 1955 - if you were to find a NOS 32609-52 coil, the holes might be either size, depending on when it was produced.
*** Jerry's frame research (over in Technical) indicates that there were 3 frames used in 1955 - frames with re-raked -52 head castings, frames with -52A head castings, and frames with -55 head castings - but all of them had the 3/8 fine coil mounts. Apparently the 5/16 coarse coil mounts were a big problem.
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"Police bikes" - What I mean by this is bikes with Police radio equipment. Knuckleheads and Panheads (and Shovelheads) came with a large carrier for the radio and antenna, a much higher output generator, a different regulator, a larger battery, different coil and spark plug wires, etc. To my knowledge, none of the K-models or Sportsters were equipped with radio gear. On our Literature page, down at the very bottom, is a section called "Historic Photographs" which show some KHs in use in the Netherlands.
Some foreign governments may have purchased/received standard Sportsters, and used them for Police work - typically for parade duty, but that doesn't make them "Police bikes". Besides the 1957 military XLAs, it appears that during the early 1960s, some Sportsters - some marked XLA, others XLB, were sold to foreign governments. Harley says they have no records of these, and they were probably sold to certain US Government agencies, which then transferred them to the foreign governments. Surfing around the web gives us some pretty iffy reports/pictures of XLA/XLBs. Whether truly XLA/XLB or not, they all look like pretty standard Sportsters.