OK, the links I provided are confusing. Let me rephrase:
4 inch at Purmerend (wartime pics - the colour fotos are posted by Folkert and supposedly show guns in the US):
This picture (my own) shows two of the 4 pieces 6 inch still at Fort NA:
This one shows what I think is a bigger version: 7 or 8 inch. It could be a 7 inch from the similar batch that went to NEI or it is an 8 inch. Nortier's article about Suriname in WW2 mentions the possible purchase of 8 inch guns for Suriname during late WW2. He says they never arrived, but he could have missed that info because he was transferred from Suriname to Australia at a certain point. The site could be the open air theatre/concrete gundeck I described above:
These are recent (Jan 08) pics of the gundeck/theatre site itself:
Will check the distances of the Fort to the mouth of the river.