Hi Nelson, Good work with that Surabaya picture! I had forgotten all about it. As Stellan wrote in his article on KNIL artillery on overvalwagen.com : 12 of the First Field Artillery Battalion on East Java's guns were high speeded aroudn 1939. Maybe simultaneously with the 16 KRA guns in the NL?
Cant answer your other questions. Charlie C did not disclose the name nor contact details of the Oz collector, but the collector mentioned to him that he and you had corresponded about the landing guns back in the 1990s. If that rings a bell with you, you will know where to find the collector and ask him those questions yourself