Good question, me not, too ! A bit strange ...
There should have been 4 versions of the WFG P 16, if those drawings are helpful, just give a shout.
.. and now, I'm looking for the sources, I used back then.
As you see, those variants differ mainly in the seating arrangement (tandem vs side-by-side) and the
shape and position of the intakes. First I got to know the P 16 from the AHS paper about "German V/STOL
Rotorcraft and Propellercraft Designs of the Twentieth Century", where it was described as an anti-helicopter
fighter with a gross weight of 1,850 kg and a speed of 362 kts.
It looks like you could use a short MU-2 fuselage as a starting point, and fitting the new wing/engines package and a new tail section with the rotors in the vertical and horizontal tails. Given that the MU-2 wings bolts to the top of the fuselage and that there is a production break just aft of the aft pressure bulkhead, it would be quite feasible.From Aviation magazine 1963,
the P-23 in details.