To Edwin_m and Gloster,
I have tried nls. The oldest map I can find there still shows the new line and therefore only the new station.
I haven't got Peter Kays book on the signalling, though I have just bought a pdf copy of his LT&SR History Vols 1 & 2. In that form they are not easy to read because they appear to be scans of a hard copy (at least Vol 1 does - I haven't got to Vol 2 yet), but they are easier reading than having no book at all so I'll have to put up with it. The problem with saying the station entrance was adjacent to Pitsea Hall Crossing is that the entrance is still adjacent to Pitsea Hall Crossing. Its just a matter of how adjacent then compared to now. Also, its possible that the original station was on the other side of Pitsea Hall Crossing, where the main part of the goods yard was, just pre-electrification - it would still be adjacent to the crossing in that position. Therefore a circa 1870 map with the detail they used on circa 1900 maps would nail the answer. However, I will try to read map on History Vol 1.
My thanks to both of you for your help
I have just found an 1868 OS map on the web. It shows (not clearly) that the western end of both the Up and Down platforms are just at the edge of Pitsea Hall Crossing, so the road (probably a rough track then) just misses them. There is a third line (a loop) round the northern side of Down platform, across the road, then connects to at least the Down line at both ends. Not sure what that was used for back then, but the western end of it was where the goods yard was in the 1960s. This means that when the new station was built for the junction, it would have been built at the eastern end of this loop, and the old platforms then demolished. I seem to remember 60 years ago that the goods yard extended into where the old Down platform had been, though my memory isn't reliable.