Thanks for the feedback. I was going for uniqueness, rather than playability! I love exploring novel ideas in games. Bridge Construction games are a favourite niche genre for me, but they're all so similar as to be practically the same game. I was trying to think of ways to mix it up - not having separate construction and testing phases was what I settled on.
If I do spend any more time on this, it'll probably become a VR game (Rift, Quest) where you manipulate things directly with your hands. That should take care of the janky crane physics!