Alec sent me some additional pictures of his pair of salem's lot first printings which also show the Clamshell cases that house them:
This final picture is quite interesting. It shows the inside of one of the Dust Jackets which has been stamped by Doubleday's office and shows the date the Jacket was either filed away or was due to be published.
The actual publication date for 'salem's lot is believed to be Oct 17th 1975, which if you take into account the fact that all the dustjackets had to be price clipped and reprinted seems about right.
Does anyone recognise the signature on this?