If I'm reading the description correctly, the cross-shafting between the engines has to be something of a design problem with the location of the engines. Not an insurmountable one but one that's definitely something of a challenge.
the Dornier P.333 was STOL experimental aircraft project of 1955,powered bu two turbine
engines,and the P.338 was also a STOL experimental aircraft project of 1957,developed
from P.333 with jet engines,all those proposals led to designed the Do.30.
A further picture of a model of the Do 30. According to 'Dornier. A brief History of the Dornier Company' , published in 1983, it said that, "This STOL transport aircraft projected in 1959 was based aerodynamically and structurally on the experience gained with the Do 29; it had rectangular wing, rigid slats and dual-slotted landing flaps. The two Dart turboprop engines were synchronized via gearbox and extension shaft. At 10.7 tonnes take-off weight, the take-off distance was calculated to be 165 m (up to 10.5 m altitude) and the landing roll was 200 m (from 15 m altitude). The cargo hold with a length of 8 m, a width of 2.3 m and a standing height of 1.8 m was configured for military use, as was the quick-change capability and the large tail loading ramp.
The Do 30 was designed as a cargo and troop carrier (up to 30 troops), as an ambulance aircraft (18 litter cases with accompanying personnel), for aerial supply (pallet dropping) and in civil use as a feeder aircraft (28 passengers), as a cargo transport and a business aircraft for industry and government agencies.
The Do 30 project was offered to the German Air Force in 1960 but was given up in favour of the Do 31 V/STOL programme.
Length: 17'5 m.
Height: 7'6 m.
Span: 22'0 m.
Wing area: 65'0 m2.
Take-off weight: 10'8 t.
Payload: 3'5 t.
- 2 x Rolls Royce DART Mk 529 each 1938 PSW/SPH"
Source: http://blogdepasm.blogspot.co.uk/2009/04/, which also lists other Dornier projects including some of its UAV programs
There is a chapter about the Dornier Do 30 STOL in the book "Dornier Do 31" published by Peter Kielhorn, Motor Buch Verlag on 25th. Oktober 2018.
Link (German): www.motorbuch-versand.de/product_info.php/info/p11073_Dornier-Do-31.html
Other projects like the the Do 29, Do P 333/1, Do P 333/2, Do P 333/8 and Do P 333/48 , which then finally led to the Do 31, are also mentioned.
I haven't bought or lend out this book so far, so I can't give a summary or post low-quality screenshots as an appetizer.