Stainless steel steering stop in situ.
It's basically a big nut that screws on the end of the cotter pin that secures the kingpin to the axle. The back of the hub stops against it, limiting the amount of turn. Pretty basic but it's a standard Ford design & seems to work.
I asked G to machine 2 flats on it, so I could do it up with a spanner. Could've done with the standard 6 flats though as there's very little room to get a spanner on it. No matter, I've just screwed it on hand tight for now, but will fit the stops before the axle goes together on the final build.
I'm going to screw a stainless steel button headed allen bolt into the back of the hub for the stop to butt against. That'll give stainless to stainless contact & mean I won't have to worry about wearing away the paint.
Many thanks Mr G.