I have the book Hs 129, Panzerjäger it does not mention the D model at all only the A,B and C models of the Hs 129. The only place I have seen the D varient mentioned is on the wiki page for the Hs 129 and this is what it says. Planned version of the Hs 129. Powered by either two 1085 hp Junkers Jumo 211 or two 1539 hp BMW 801 to improve its performance. No prototypes were made.