The Harold Tower protect engines

101 and 105 were once the Harold Tower protect engines. Now 102 and 104 have the job. Why did the LIRR go through the time and expense of swapping out the M-1/M-3 couplers and the ASC from 101/105 to 102/104?

Another thing: When was the change made?

Mid to late 1990s the change was made.

Just a guess: they needed to work on 101 and 105 couldn't pull them from that service, so they fixed up 102 and 104 for it then pulled 101 and 105...