I replaced mine as a straight replacement with a front ultegra dp wih no problems. It might be worth measuring just to see if you need a deep drop
I think you are writing about something quite different here. Looking at the picture of your trikes, the road Longstaff has a front brake fitted through the fork crown just as is normal on a bike, then has a cantilever behind the fork crown. Hence you can do what you like with single or dual pivot brakes.
As I read it, Zipperhead has the circumstance where the cantilever is mounted in front of the forks with a single pivot brake on a stalk. In the same place you have a centrepull on your Rogers.
Now- it is easy to replace the centrepull on the stalk by a DP. It is not easy (in fact I don't know how to) replace the SP on the stalk with a DP. The reason for this is that George integrated the central bolt of the brake into the stalk, hence any brake must fit that and be secured by a nut at the end.
However, you can fit probably any SP brake to the stalk. Mine started out with a 1980 Campag brake and has now got a very much newer Shimano SP. With decent cables and routing etc this is a powerful brake.
So, Zipperhead - I don't know.