Window locks weren’t standard on the Series I – in fact, they weren’t fitted for a very long time. Screw-to-close window locks were fitted on panel-built Series I Station Wagons and also on deluxe 107-inch and 109-inch pick-ups – but they’re hard to find now. You’d think they may have been an optional extra, but that doesn’t seem to have happened.
There were two types of Series I window lock, as there were two types of door top. On the earlier type, the window channel is exposed; on later ones it’s hidden behind a shoulder in the door-top frame. This change happened about the same time as the change from 86/107in wheelbases to 88/109in wheelbases.
Your vehicle will have the early door tops with the exposed channel. It’s possible to fit Series II push-and-turn locks on the later Series I door tops but, for fitting on the early door tops, you’ll need to do a bit of metal-bashing: bend the lock’s support bracket to suit the early door top.
Should be possible, given a bit of patience.