A quick trick for reciprocal headings is to add 2 to the first digit and subtract 2 from the second digit (or vice-versa). eg 315 135 or 253 073.
I use the same trick, but I find "Add 200 and subtract 20" or "Subtract 200 and add 20" is easier for me to figure out.
As IO540 says, it doesn't strictly work for 181 to 199, but it easy to convert a result like 375 to 015.