what about Sea trout fishing by Charles Maclaren? a master before falkus, easker1
A really good book from 1963, but a year after Falkus's first edition of 1962.
Both Mclaren's and Falkus's books are really excellent but their content is really localised . . . as most seatrout books are. Morgan and Harris's 'Successful Sea Trout Angling' is also localised to Welsh circumstances but far more 'modern'.
For a more up to date assessment of sea trout fishing, I'd recommend Stefan Jones', 'Sea Trout, Tips, Tricks & Tribulations' 2017.