IC-740 is old aged transceiver in 1980's.
But once after you experienced receiving performance, you can never leave it alone.
Today, I got FL-54 (270Hz CWF) inexpensive only USD30 from Japan Yahoo Auction.
If you read Icom installation manual, you feel so complicated explanation.
Anyway, only one change for the wire No.13(blue) of J36 connector inserting to the any pin of J6 or J7 or J8 brings you completed option CW filter wiring change.
Last difficulty is CW filter will not be activated if you depress only FILTER swtich.
You have to depress IF/PBT switch (means PBT ON) and then FILTER swtich ON for CW filter use.
Hope you enjoy CW operation on IC-740 !!