Today's progress:
... Has been minimal because once again we have been tasked with grand-kid minding.

However, I managed to sneak out and do a few bits.

First I reversed the drop-outs in the MBB forks to try to prevent them climbing off the axle in use. Basically I inserted a plate in the existing drop-out(s) and then cut through from the other end.

Then I tidied up all of the debris left behind on the forks from the removal of seat-stays and down-tube.
It was a pain welding the previously "hidden" section of the seat-tube to the bottom bracket. I also filled in the vent-hole in the BB-Shell that had been covered up by the down-tube.
This provides me with a reasonably tidy MBB fork assembly.

When assembled onto the front forks it looks reasonably tidy. Now, I will try and get an upper seat-mount made so that I can get an opportunity to sit on the trike and find where the BB will need to be located and how the seat tube on the MBB forks will need to be angled to connect with the handlebar goose-neck.
As I have short little legs this may present a few issues as that MBB looks to be a L-O-N-G way away from where I will be sitting.
I might even need to cut the seat-tube shorter, as well as angle it. I also have a QR seat clamp of the right size so adjustments and tweaking of the relative position of the MBB should be easy to do within a limited range of motion.
I still need to make a derailleur hanger for the front forks and sort all the Front changer stuff out too.

But, its coming along OK really.