The collection includes the original Union Jack bunting from Queen Elizabeth's coronation, crystal goblets and a crystal bell made in honour of Prince Charles and Diana Spencer's wedding, original sketches of the Queen's wedding dress, various china items and specially engraved coins.
He has also collected souvenir books from King George VI's coronation in 1937 and hundreds of magazine clippings on all matters royal.
"No-one's allowed to touch those. They'll all be in glass cases," he said.
"I think for a lot of people this stuff will bring back memories. It will take them back to the Queen's coronation, or her wedding, or when they saw her on her New Zealand visit.
"There's a lot of hype around being able to say, 'I saw the Queen."'
Mr McDean, an interior designer and painter, has spent years gathering royal memorabilia and describes himself as an "obsessive collector" - with his two other passions being miniature tea sets and attractive bed covers.
He confesses he is not a monarchist, but has been an active follower of royal commentary over the years - and enjoys the royal family's celebrity status as played out in the media.
"I do follow what the royal family are up to in magazines like Women's Weekly," he said.
"It's good gossip and makes good reading. I tell people I just buy the magazines for the crosswords, but that's not quite true."
However, Mr McDean is as interested in the history as the gossip.
"These are all pieces of history. Royal history is still a part of New Zealand life. It'll never stop. Even if New Zealand became a republic, I think there will still be a big percentage that will still be royalists."
The exhibition will run alongside the Eketahuna Art Group's "Trash and Treasure" event, where people can buy donated household goods - but Mr McDean stresses that the royal items are not for sale.
"People love the bunting, for example. They've been trying to take it off me for years. But, it will be passed on to my children. Hopefully they'll want it."
The exhibition is from October 25 to 27 in the old post office building in Eketahuna.