I recently acquired this Manta 19 (1973, #205) in Dragør, just South of Copenhagen. Immediately taken with her beautiful lines and original retro orange gelcoat, I'm trying hard to ignore the facts that the centreboard needs to be replaced, the ballast keel renovated and all deck hardware rebedded ... and who knows what else. But she's worth it, isn't she?
On a German bulletin board I found a technical drawing of the centreboard by user "Soros", that I've used to make a 6,5 mm plywood prototype, that seems to fit like hand in glove: https://www.segeln-forum.de/board20-vorstellungen/board22-ich-bin-neu-hier/56892-manta-19-berlin/. The dimensions differ a bit from the drawing of "Sophie"'s centreboard but was very easy to get right - and it seems to be spot on.
Unfortunately, the drawing in the thread can only be displayed after you have registered as a user - and I don't want to step on any toes by making a copy to put on this site.