Update : i packed up the rose joint and its cover with grease, rebolted the A-arm, and as expected, no more play ! That was really the bolt that wasn't tight enough... Good thing ! But I noticed that there 's some vertical play in the lower ball joint of the king pin... That's not normal , isn't it ?
Other point : now the steering arms are bent, the track rod ends have to be shortened, because they are at full stop, and the arms are not bent enough to suppress the hexagonal extension
... So I cutted 11mm on the new track rod ends:
It doesn't weak the stuff as the whole thread of the extension is still contained in the track rod end... It's a common modification on MGs, documented on Moss website...