When I purchased my sandman back in 1992 for $5600, it didn't come with a engineer certificate so I got one and registered it as a ute ever since. The engineer said the conversion had been done properly. When they did it they were careful not to touch the rest of the body even managing to keep the original stripes as far as I know.
I have got a recent quote to fit the turret only (No painting other than undercoat - for $4,500) Seemed like a fair price to me ? The bloke seemed to know what he was doing. My main concern about having work done on the sandman is leaving it in some one else's garage. I'm paranoid about 'losing' original parts off it or just having the whole thing go stolen.