Looks to me like the pedals are now considerably further fwd than in the earlier pictures and so the boom can be a bit lower ? before pedal strike ?Update 7th Nov 2020:
I did a tiny bit more mock-up and messing around with the trike today.
It seems that with the seat in the ideal place on the main keel I will indeed have the same relationship/distance between the seat and the pedals as exists on the Tadpole.
Next job is to try and sort out how to add some steering capability. USS and a rod attached to the forks seems about right.