Will units from any other of the bikes fir 1200LT ?
NO , you need to stay within certain years range for your model. There are 3 types altogheter:
1) K1200LT of 1999-2001 (for USA market) having ABS2 units - these have no servos and are very different than later models.
2a) K1200LT of 2002-2004 (for USA market) have the iABS units with servos - modulator is installed Vertically in frame.
2b) K1200LT of 2005-2009 (for USA market) have the iABS units with servos - modulator is installed Horizontally in frame.
Although internally most parts are the same for the units of item 2a) and 2b) above (2002 to 2009 models), because of external design changes they cannot be interchanged or installed into other years.
NOTE that if your K1200LT was built for a market other than USA (Europe, Canada, Australia), the years above will change slightly as the design change was offered in 2001 instead of 2002 in other countries - so item 2a) above would become 2001-2004 for 1st generation having iABS.
FURTERMORE.... Most Boxer models of 2001-2004 also had a similar iABS unit with servos, but the mounting was a bit different. Again, many of the internal parts were the same. All these iABS modulator were built by FTE in Germany custom specs for BMW. They both had a somewhat "secret" arrangement where FTE would not sell units or parts directly to anyone else.