Today I found a picture showing Dire Straits live in 1977, before they recorded their first album. At this time the famous red ‘Sultans’ Strat was not refinished to red yet but still had the bare wood finish in which Mark got it (probably earlier that year). There are a few pictures around that show the guitar with this finish but all of these are of rather poor quality (and all are only black and white). On only one you can actually see a bit of the wood grain, and this only shows a part of the guitar.
This picture now is by far the best available of the Strat with the wood finish. We can see that it already had the black volume knob (or whatever purpose the knob really had). Also it seems that already at this time the middle poti had a knob labelled with volume instead of tone, something you can see more clearly on many later pictures.
The picture strongly suggests that the guitar has an alder body (alder was the common wood for a ’61 Stratocaster, but some finishes like e.g. blonde often had ash bodies). It looks as if it is a two-piece body, and the seam is almost in the center, approximately at the height of the d string. Two-piece bodies are very common but the position of the seam varies. The guitar does not look very glossy but I don’t think this allows us to tell if it was some wax&oil finish or clear laquer. Unfortunately I cannot tell with certainty if it already has the DiMarzio FS-1 pickup (the length of the pole pieces is different compared to a stock vintage Strat pickup) but listening to the solo of Eastbound Train from the Hope & Anchor, which was recorded about the same time, suggests that it had.
In the background we can see the 1961 Vibrolux and we can clearly see that Mark used the bright channel of the amp. Both channels are basically identical with the exception that the right channel has a treble bleeding capacitor over the volume poti. This capacitor became switchable (‘bright switch’) later (with the introduction of the blackface amps) but on the Vibrolux one channel is without and one with the capacitor.
Note that David’s guitar also has a wood finish (and also John Illsley Precision Bass). I am almost sure that both David’s and Mark’s guitars were refinished at the same time (about late summer 1978, David’s guitar became black then). David seems to play an unwound g string as it seems, I remember seing him on some 1978 pictures with a wound g string on his Strat. The vocal microphone seems to be a Sure SM57 (these were dark/silver before they got the dark finish they had later). This mic is normally not used for vocals but Mark did so on many gigs in 1978/79. In fact if you sing at rather low volume, you can get it a bit louder on stage before getting feedback than e.g. the more common Sure SM58.
Dire Straits only played a few first gigs in 1977 and these were at only five different venues (Rock Garden, Dingwalls, Hope & Anchor, Champers Wine Bar, Loughton College). I wonder if it might be possible to tell from where the picture is, the wall in the background right suggest a rather small pub but my googling for stage pictures of these pubs was not successful yet, maybe someone else has some idea.