I'm not sure if this is working as intended or not, but the girder blocks currently have 6 rotations. And that doesn't allow for the top side to be on all possible sides or directions. The similar shipyard block has 24 positions when rotating it around. It seems like their rotations should be similar, but they're not.
Also, when the top face of the shipyard block is facing up, it can't be made to line up with itself when traveling in the direction of the red symmetry plane. I've never had a need to do this... but just happened to notice it after messing with the girder block.
I feel kind of confused now. I just wanna decorate with girder blocks.