Thanks Max, I am on a steep learning curve!
I have looked at the front end geometry and taken the following photo
Front end geometry I may well have labelled the components incorrectly, but I needed them in order to be able to discuss.
From what I can see, I think there is only a slight height adjustment possible (to level front end), between frame and subframe, and no way for it to pivot. The bolt that you saw in previous photo (looking from the front of mower) attaches the subframe (or crossmember) to the frame.
I forgot to label it, but there is a bracket that hangs down about 50mm with a bolt in it, but currently doesn't appear to serve any purpose. There is one on each side so I assume they could be used to mount something? In the photo, it is partly obscured by the nut on the left end of steering rack.
