+1 to that. Contacting the DVLA can end in a can of worms. The A, b, C thing was very informal and don't assume that the years were exact. E only ran half a year.
If its not been on a SORN do that first, that will get you in the system and means they have to issue a new log book free if its on an old style book. When was it last on the road? All you really need is the reg, after that its about getting a replacement log book. Can the executor ask for a replacement then you can do a change of owner?
There's no great need to sort out the numbers and age, it is what it is after 60 years, It wasn't uncommon for old unused reg numbers to get assigned later to use them up.