IGN.com http://atu.ca/546b

..the Ecto-1 [eBay auction: http://atu.ca/Ecto1 ] was
acquired after Universal Studios had stripped the car of
most of its component and were planning to sell it.
BenTrodGarage and Co. managed to swipe the car along with
the original roof rack and light bars before it could be
sold as an ambulance. They were able to reassemble the car
back to its original form and replace any missing parts and
nuances.

On the mechanical side of things, the car apparently packs
a Chevy 350 engine with a turbo 400 transmission...

To ensure authenticity, BenTrodGarage apparently has the
original bill of sale from Univeral Studios and a copy of
the original title...