The front derailleur needs a tube on which to mount. This ended up being a piece of water pipe that was bored out to a reasonable wall thickness. The pipe was then tacked in place on the bottom bracket as the derailleur range of motion was tested prior to final welding.
The used front derailleur is a top pull design. So in order to not have an excessively long mounting tube a special bracket was made to support the cable end. It is made from a piece of steel flat stock and a cable end braze on piece. The braze on piece was brazed into the bracket and the whole thing welded on with some intermediate test fitting. 
Afterwards, I flipped the trike back up on the buckets for more work. However it was a bit too soon and I am a bit too clumsy, so the bracket branded my left arm. This is what it looks like a day later.
You can also see one of the sets of water bottle mounts in the photo of the crank assembly. These were more braze on bits. They require a 1/4″ hole in the tubing and are an M5 thread.
The next pieces were a rear mount for the tail light and adding the parking brake. The parking brake, seen below, was a down tube mount gear shifter in its previous life on my dad’s old bike. It was trimmed down and brazed onto the frame under the seat. It still needs a dip in rust remover and a new cable but it works.
So here is the nearly finished trike. Ready for test rides, body work (more grinding and some filler) and painting.
Ready for the next test ride (minus helmet). One water bottle mount (stolen from my road bike) in place.
There is still tuning required. The front derailleur does not like to shift onto the lowest gear and the rear skips when I pedal hard. I don’t know if it is an adjustment issue or that the used gear cluster is too worn. With the recumbent, there can be a lot more torque applied than when upright. I can make it up the driveway, but the speed is limited by rear gear skipping (darn).
The top speed riding around our neighborhood so far is 23 mph. Not great, but not horrible either. The trike tends to pull a little to the right when hands free. I will probably add a tiny bit of friction in the steering linkage somewhere to account for this. I really don’t want to cut off the right front wheel arm and tilt it a few more degrees to add more caster. I see 9 degrees forward on the right vs the 10.5 on the left as best I can measure.
Now it is time to tear it down, cut down the front rail tube, do some body work and paint it. There are also some parts to 3D print, including new chain idlers. The Northern Tool idler pulleys are too narrow and generating lots of metal shavings on the chain and I am sure excess friction as well.