Mr Coleman was the only non-Northlander working on the project, while Mr Mason formed the complex bodywork, which goes from concave to convex and back again.
Fiat made 2411 of the luxury 519s between 1922-1927 and there are only two left, with this car being the only one having the stylish boat-tail rear.
Hans would not reveal how much he paid for the car, or how much he sold it for, but said about $400,000 would have been spent on it by the time the new owner added his own finishing touches, including painting the interior and a few fittings.
"We normally do total restorations, but this was a regular client who wanted it in this condition so he could then add the rest," he said.
Hans said the car was imported to Australia 88 years ago.
"They were well ahead of their time when they were made, too. She had overhead valves, hydraulically assisted brakes and on all four wheels, and an adjustable steering wheel."
Hans said most people thought of Fiats only as small cars, but the 519S was the second-largest Fiat ever, behind a 6.8 litre V12 monster produced in the 1920s.
Dion had been putting the 519S through its paces and said it drove really well.