The powerplant for the D.H.123 - the de Havilland Gnome P.1000 turboprop - had an interesting shaft arrangement. Here is a bit on the P.1000 from
Flight 18 March 1960:
"D.H. Gnome P.1000 Free-turbine turboprop. Ten-stage compressor with variable-incidence inlet guide vanes and first three stators, annular combustion chamber with 16 burners, two-stage compressor turbine, independent single-stage power, turbine driving through rear reduction gear, high-speed top shaft and front reduction gear to suit propeller speeds from 1,245 to 1,550 r.p.m. Overall length, 87.3 in; height, 31.55 in; width, 17 in; dry weight, with starter and accessories, 555 lb; mass flow, 12.4 lb/sec; pressure ratio, 8.3:1; max rating (5 min.), 1,000 s.h.p. + 144 lb thrust at 26.260 r.p.m. (20,000 power-turbine r.p.m.) with s.f.c. of 0.669 lb/hr/s.h.p.; recommended cruise, 800 s.h.p. + 120 lb at 25,120/17,000 r.p.m. with s.f.c. of 0.728; the P.1200 will have corresponding ratings of 1,150 and 900 s.h.p. with sf.c. of 0.657 and 0.71.
https://www.flightglobal.com/FlightPDFArchive/1960/1960%20-%200370.PDFFlight 20 July 1961 reported that "The first P.1000 ran in September 1960, and a Dakota is now being fitted with two of these engines for flight-test purposes." Anyone know if that TurboDak actually flew?
https://www.flightglobal.com/FlightPDFArchive/1961/1961%20-%200980.PDF