First of all, it is a No 4, not a Mk 4. The most common are No 4 Mk I and No 4 Mk I*, though there are other variants. Lithgow never made these. They were made in Britain at one of three plants, and wartime production tend to have rather ordinary external finish (machining marks, painted finish) but are strong and work well. Most are No 4 Mk 1*, which was somewhat simplified for more rapid production.
They were also made at Long Branch (Canada) and in the US (by Savage). The latter two types tend to have better cosmetics, and are No 4 Mk I*. They are also prominently marked as to their origin, so the lack of much in the way of markings suggests a British one.
There was also No 4 Mk II, made in the UK, most post war, and a lot of these hit the market some years back in mint unfired condition, and they are very nice if you can find one, though you'll pay more.
Other less-common versions tend to attract a price premium, if unmolested and in good nick.
There are several versions of rear sight, including a nicely machined version with click adjustment for elevation, a couple of simpler pressed steel versions, with a sliding mechanism for elevation, and a simple two-distance flip over version, as the set-up was simplified as the war progressed. They are easy to swap over though.
I can't comment on the prices they are attracting there. FWIW I have a Savage version myself, and have owned a British No 4 Mk I. Of the two I prefer the Savage, and a Long Branch would be about as good.
I had one of the ones made by Savage. It was actually pretty accurate too. Still kicking myself for selling it.
