Headset - for a trike I would go for the BBB I showed. Reason being that dependant upon use a headset can take a hammering in a trike so it would be nice to be able to replace bearings easily instead of the whole headset. This is why for decades I used the old Stronglight A9 with replaceable bearing tracks.
Brake mount - Mavic used to make an adaptor plate to relocate canti studs. Do an internet search for "mavic V brake adapter" and you will see what I mean. This can be mounted behind the forks, hanging from the through bolt from the brake on the front of the forks. This will enable you to play around to see if a mini V will fit/work for you. There were nicer plates made for mounting V brakes on BMX. DNA was a brand, but these are now rarer than hen's teeth. I have a DNA one in use on a Ken Rogers small wheeler I built as a project. I don't do photo hosting so cannot show any pictures here.
I have a Mavic adaptor that has been in my box of bits for many years. I will donate that if you want it, just PM me a mailing address.