IIRC (from being a kid) Harry was 256 color and DN2 wasn’t quite. Also it felt like it had much better frame rate. But I’m sure that could be engine evolution too. Interesting, I hadn’t ever thought of the connection before.
Though the “hot babes stuck in alien pods” from Harry showed up as a central plot point in DN3D.
I mean, I could be wrong as far as Harry and DN2 sharing an engine, OTOH Apogee did a -lot- of engine reuse (Bio-Menace used a CK4 variant, Monster Bash using an evolved FAST..)
Although, mea culpa, DN1 engine is not necessarily CK but the programmer has credited Carmack in helping with the drawing assembly...
Harry was written by an Australia, John Passfield, on his own and published by apogee (I forget but apogee might have provided some art support). John is still making games today!
Though the “hot babes stuck in alien pods” from Harry showed up as a central plot point in DN3D.