Hello,
I'm new on here, but I had the pleasure of meeting Mr King and his collection at the Grantham Model Rail show last weekend. The Streamlined mountain is very impressive. Your Grantham layout is also a delight and i've read all 25 pages of the thread!
I have also studied the real location on and off for years as I am born and raised in this dear town. I noticed that you were intrigued by the signal at the south end of platform 5. It is possible that this was commissioned at the same time as platform 1 was extended northwards during the second world war. Allow me to explain, it would seem that until the line from Lincoln was opened, all trains from Nottingham and Boston would terminate in what became platform 2 on the up main! When the Lincoln line opened the new bay platform 1 was brought into use along with a connection from the Nottingham line. I suspect that from then on trains from Lincoln, Boston, Nottingham and Leicester would terminate in platform 1. Mind you at busy periods no doubt trains would still terminate in platform 2. Looking at various ordance survey maps and photographs, platforms 4 and 5 were used for Northbound departures. When platform 2 was extended northwards this cut the connection from the Nottingham line. The facing crossover on the Nottingham line was installed to allow Nottingham trains to arrive at platform 5. I've no way of telling if trains terminated in platform 4. Consequently, the need for a locomotive release at the south end of platform 5 comes into its own. This allows a locomotive to escape back to the North signalbox and onto the shed. Also installed at this time is an additional trailing crossover on the ECML to allow trains to depart platform 1. I have also spotted that an additional through line was installed in the down goods yard and a connection from the shed yard towards Grantham South signalbox!
Finally, with regard to the features at the south end of platform 5, two photographs in the following books, "LNER 4-6-0's at work" page 108, the top picture shows the connection into the adjacent carriage siding and "Eastern Region Steam Twilight, part one" plate 202, shows Mallard in platform 2. On the extreme left of the picture, you can see the signal post on platform 5 next to the so called glass house!
I hope my ramblerings have not sent you to sleep and that this helps you with the layout. If i can help in any other ways drop me a line
Paul Mellor
Flying Fox 34F