Thanks hamster, the stem is indeed past the max line. I've not ridden it like that, but I assume whoever owned it before me had it like that for a while
I started to take it apart this evening and everything seems to be in decent shape. The handlebars are covered with surface rust under the tape though, but I'm hopeful it'll come off.
The wheels will need replacing as they're warped and the saddle is a mess so that's going too, but other than that I think it'll turn out pretty well.
It would be nice anyone had a rough idea of the year it was made. I'm curious to know if it's older than me!