Question: In what year did the museum, where two South Australian Railways 400 class locomotives are preserved, move to its current location?

Context paragraphs:
South Australian Railways R class: The South Australian Railways R class, later upgraded to Rx Class was a class of 4-6-0 steam locomotives operated by the South Australian Railways.

South Australian Railways 620 class: The South Australian Railways 620 class was a class of 4-6-2 steam locomotives operated by the South Australian Railways.

South Australian Railways 500 class (steam): The South Australian Railways 500 class was a class of 4-8-2 steam locomotives operated by the South Australian Railways.  They were rebuilt as 4-8-4s.

South Australian Railways V class: The South Australian Railways V class was a class of 0-4-4 steam locomotives operated by the South Australian Railways.

National Railway Museum, Port Adelaide: The National Railway Museum, Port Adelaide, South Australia, is Australia's largest railway museum with over 100 exhibits on display, primarily from the Commonwealth and South Australian Railways.  First opening its doors in 1970, the Museum moved to its larger and current premises in 1988.

South Australian Railways 520 class: The South Australian Railways 520 class was a class of 4-8-4 steam locomotives operated by the South Australian Railways.

South Australian Railways Z class: The South Australian Railways Z class was a class of 4-4-0 steam locomotives operated by the South Australian Railways.

South Australian Railways X class: The South Australian Railways X class was a class of 2-6-0 steam locomotives operated by the South Australian Railways.

South Australian Railways 400 class: The South Australian Railways 400 class was a class of 4-8-2+2-8-4 steam locomotives built in the early 1950s.  The 400 class locomotives mainly hauled mineral trains on the South Australian Railways' narrow gauge Broken Hill line from 1953 to 1963, when they were replaced by diesel locomotives.  They operated as far as far south as Port Pirie and Terowie and as far north as Quorn.  The 400 class was temporarily returned to service in 1969 while the diesel locomotives were converted to .  Two have been preserved, 402 at the Zig Zag Railway, Lithgow and 409 at the National Railway Museum, Port Adelaide.

South Australian Railways W class: The South Australian Railways W/Wx class was a class of 2-6-0 steam locomotives operated by the South Australian Railways and later the Commonwealth Railways.

Supporting paragraphs: South Australian Railways 400 class National Railway Museum, Port Adelaide
Answer: 1988