using 3ds Max 2013 64-bit and 4ds import plugin i imported H&D 2 and Sabre Squadron missions (all Single Player maps except Training) in *.4DS format and then converted them into *.WRL format and finally into *.I3D format that could be opened in HDD Editor.
Credits for NilsZ for letting me know about this method!

You will also need to have installed H&D 2 + Sabre Squadron and unpacked textures from the game Maps.dta archive (i.e. using DTA Unpacker) in order for the 3ds Max 3.1 / HDD Editor to display them on models / visuals.
Those attached maps could be used i.e. as a basis for creating new H&D Deluxe addons.