The waypoint calls would possibly be individual to the squadron or even each aircraft and given in morse of course, hence the brevity. The sequence of letters may have been read from an overlay grid placed over the nav chart - think early football commentary on the radio in the 1920s 'and back to square one'.
There is a web site that provides reanalysis data of historical synoptic charts at
https://www.theweatheroutlook.com/twodata/reanalysis.aspx which would provide the likely weather and wind direction for the night of the operation and allow heading and groundspeed calculations to be found for a given date.
For doing the maths have a look at an online simulator of the traditional type of air calculator at
https://e6bx.com/e6b/ . It uses the same principles as the hand held nav computers. Rather than do it with pencil and ruler why not use Google Maps to plot the co-ordinates and distances and then calculate the airspeed to groundspeed changes to get the time to fly each leg? Do you know whether they climbed at base before departing (as per 8th USAAF) or climbed en-route?
You can use 160 mph IAS for the climb to 12,000ft and 155-150 mph IAS above that. Once at cruise height 160 to 170 mph IAS on the outward and 160 mph IAS on the return leg seem to be the standard operational procedure. The Lancaster would climb at about 1,100 ft per minute or about 45 minutes to reach 28,000 ft. Info from Lancaster pilots notes available online.
To get the TAS (True Airspeed) from the IAS (Indicated Airspeed) add 2% for every 1000 ft of altitude. This calculation would normally be provided by the circular slide rule on the back of the 'Computer'
If you don't get anywhere with the maths it may be something that the General Aviation Group at the Royal Institute of Navigation may be interested in or give you a pointer to someone who would be.
