Update 29th April 2020:
Today was a wet and windy day but an opportunity presented itself to push the tadpole out into the damp and pull the delta apart to do some more work on that.
I did not get too much accomplished but every tiny step forwards is a bonus. Today I managed to mount a front mudguard. It is a tight fit but the tyre does not rub anywhere and it seems to be a good rigid mounting.
The mudguard is on backwards (I don't think it knows or cares) and what is now the front end will be bolted to a sturdy wire bridge that is fixed on M6 bolts through the frame and the dropouts.
The rear end (that had a convenient mounting bracket riveted to it) is tethered by a small section of 12 x 3 mm bar threaded for an M5 bolt. This may leave enough of the mudguard exposed to have the actual mud-flap fixed onto it.
Then I removed all the cables and the handlebars and started to measure and cut the steel tube for the additional supports for the pivot to prevent the "rocking" of the front frame on the pivot mount.
And then it started raining properly and I was forced to come indoors. If it brightens-up I may venture back out again.
EDIT @ 17:39PM
Well it did stop raining (a little) and I ventured outside to try and place additional attachment points support on the pivot.
It was a horrible job, I am not in the least delighted with it, but it is done.
From the front.
And from the rear.
NOT the prettiest job, but as it is performing a "belt & braces" function, I don't care. It can be as ugly as it likes. So there!
I am losing the will to live with this trike.