By this stage the rear fenders are a better shape and I had covered the rear axle gear too

Underside scooped out so it can be resin cast

A bit more progress, but it's frustratingly slow to get all of these things right! Exhaust is done here but this was a huge task as the muffler didn't fit under the bodywork and matching the first pipe's curve to the front fender was difficult as the pipe then needed to curve into the hood. The other pipes were tweaked to fit as the same radius didn't quite look right although the pitch of the 4 pipes is even

More difficulties as I did image searches of the car; there were 6 cars built for the movie (5 still exist), they've all been modified over the years and there are also some replicas around too. I got gradually better at spotting the differences! Here's a potted history of the movie cars.
CHITTY 1
Pierre Picton owned GEN11 which was the primary road going vehicle, the car which Dick Van Dyke rolls out of the workshop. It was used in all bar two UK location driving shots. They drive to the beach in the vehicle. It is the car which sits on the beach, the car which delivers Sally Ann Howes to the gates of the Scrumptious estate, and the car which takes chase after the zeppelin. It is the car the Potts drive home in from the beach and the car which forces CUB1 into the duckpond on every occasion. Pierre owned the car since the early 1970's after it completed its duties promoting the movie in the UK.
CHITTY 2
This car had vertical bars behind the radiator grille. The steering wheel is considerably darker in colour and the metal on the dashboard is matt finish rather than shining. It also had an engine and a second steering wheel on the floor which was a feature used in one scene. It appears rarely in the movie, though may have been the first car off the production line as it appears in the first scene that was shot involving Chitty. It also is heavily featured in pre filming publicity shots, and is the car test driven by rally driver Paddy Hopkirk.

It appears in the shot where they are driving beside the train, in the shots where they are being harassed by James Robertson Justice from the car behind them (first driving scenes which were shot), in one passing shot on the way to the beach, and in the scenes shot in Bavaria where it comes to rest under the aqueduct and later when it is towed by infantry horses through the Town Square and into Neuschwanstein Castle shortly thereafter. It is also the car which drives itself into the castle to rescue our heroes during the overthrow of Bombhurst, and the car which descends the red staircase in triumph.
This car was in the USA immediately following the movie for promotional purposes. It vanished for a number of years only to turn up at the Cars of the Stars Museum in Keswick, England in 2000 which is where I first saw it!
CHITTY 3
This car appears to have had a removable chassis and was lighter in construction. From all accounts it was primarily mounted on a trailer for close up driving sequences and was used in the studio for some process flying and floating shots. The wings it sported were slightly different to the wings of the "flying version" (Chitty 4) It is also used in the studio pool for some shots during the transition to the water car sequence. Pierre Picton also acquired this version in the early 70's. It was the second UK promotional vehicle, and had an engine added for this purpose. Mr Picton modified it somewhat to become part of his circus act. In the mid 1970's it was sold to Heathfield Wildlife Park where it was on display in the park's motor museum. In 1978 it was sold to The Rotunda in Folkestone, and in 1980 was auctioned at PInewood Studios where it was purchased by private collector Anthony Bamford of the JCB family.
CHITTY 4
This is the car with wings. It was the photographic model for the promotional image from the movie which featured on posters and merchandise. On screen it is the car which sprouts wings. It is used in a bulk of the process studio flying shots, it is the vehicle which lands in Vulgaria and the vehicle which sprouts wings and propellors in the castle forecourt before they leave Vulgaria.
The wings had a leading edge metal framework which housed folding propellors. This framework was covered by a rolling cover which was in place when the car sprouts wings and first flies from the cliff. This car also promoted the film in the USA, and was present at the New York opening. It was later sold to and appeared at The Cavalcade of Cars exhibit at the (now closed) Gaslight Village Amusement Park in Lake George, New York. It then was a feature at a Chicago Restaurant "The Retreat" before the venue went into receivership. The car was then auctioned in 2007 and sold to Ralph Spencer of Florida.
CHITTY 5
This car was built for one scene, the transition from car to hovercar. For this reason, costcutting is evident with aluminium being used on most features (radiator surrounds, exhaust pipes, windscreen) in place of brass. Aluminium may also have been used to stop the discolouration of the brass and copper in the sea water. This car was unceremoniously placed in the sea off the coast of France, with an air compressor nearby. The cast were ferried to the vehicle in motorised dinghys and on cue, the car backfired, two panels at the rear opened to release a propeller and an inflatable flotilla was pumped full of air under it pushing the hinged wheels outwards. At this point it was replaced by another car mounted atop a speedboat. Chitty 5 promoted the film in Australasia. It was star attraction at the 1970 Motor Show, and toured the country right through until 1974. It reappeared in 1983, the property of Luxafles, a canvas awning company and was regularly seen alongside their displays in shopping malls and promotional events. Luxafles fitted a GM Holden engine into the static vehicle. In 1991, it was sold to Peter Nelson of Cars of the Stars in Keswick, UK, and in 2000 he sold it to Barbara Broccoli's EON productions. EON refurbished the car, painted some of the aluminium features gold and used the car throughout the world to promote the stage musical. This is the car which was famously banned from the Norwich Parade as it was not in possession of an MOT (roadworthyness) certificate.