I have also just checked your "basket case" with the Douglas Club register and would like to confirm that CCEW is quite correct.
It is either an A31 or A32, ironicaly we have details of others, your frame number is between the last A31 but before the first of our A32 records! so your guess is as good as anybodies. More of interest is that the engine number also falls into this bracket suggesting that it is probably the original engine fitted.
In the era in question Douglas did not match the frame and engine numbers, we assume they were made in batches numbered and then assembled with whichever came to hand from each batch.
The other variable is that many bikes of this era are dated as they were registered and so can vary a year or two depending on their pre sale history.
Your machine does not appear in our register, we would like to add it assuming you have no objection, we never reveal any owner details without the owners permission.
We are also very interested in adding the gearbox number as this information can be very helpful to anyone trying to rebuild, particularly from the basket!
Good luck with the project, they make a great "classic" runabout assuming you do not wish to "burn rubber!"
Now the Ad, you should consider joining the Club for assistance and some spares, sadly not a tank or wheel rim! Details from the Club website douglasmcc.co.uk