My money is still on a cracked head, both the heads.
Luckily I didn’t bet the farm.
Re; the head brace, keep in mind that it is not supposed to strengthen the frame but to merely stop vibrations.
So if it was the headstay causing the problem then you might want to give the frame a good inspection as it may be flexing more than normal.
Glad you got it sorted, all other problems will now seem insignificant.