They are IBC hydraulic rim brakes. Not Magura.
I have some on my Fat Chance.
https://www.thebicycleguys.com/products/ibc-hydroceps-940-hydraulic-rim-mountain-bike-brakeset-970-g-new-in-box-nos
Yes on the flat.
Reluctant to use my lambretta, open carb and gravel roads don't mix well. Might have to put a bigger jug on the smallframe. Keen for the ride.