There is little known and even less written down concerning the conversion of the Viva HB by Crayford Auto Developments of Westerham, Kent. This includes the actual number of cars converted.
History
I shall start before the Crayford HB convertible actually appeared. Back in April 1967, David McMullan (MD of Crayford Auto Developments Ltd) purchased a new white HB Viva SL90 for his father. Once acquired and viewed, plans could then begin in earnest as how to chop the roof off.

In the mean time Crayford’s used the car as their flagship for the HB range, launching the ‘Viva Prince’. This had a Black Vyinde roof covering, extra sound proofing and an Airflow extraction system, which consisted of a pair of stainless steel external grills fitted to the rear roof pillars. Also twin extraction grills were fitted inside the car on the rear parcel shelf to keep the rear window demisted.

On the exterior of the Viva, the sills were painted with heavy matt black paint and finished off with a chrome moulding strip running the length of the car. This gave the effect of making the bodyline thinner and reducing the stone chip damage on the sills. Most of the panels were treated to sound deadening and the bonnet had a distinctive black centre line. Each car had a special ladies cosmetic case fitted, but as no one has ever seen such an HB the actual position of the case is unknown. To boost the rear extraction system an electric demister motor was fitted to aid the demisting of the rear windscreen. This little lot came to a price tag of £95.

Then there was the 'Viva Prince GT' at £169. This consisted of the Prince conversion, plus a Blydenstein Weber carburetor conversion with a special exhaust system. Which meant the car was a full 7 seconds quicker than the standard SL90 car in respect of the 0 – 60 mph time. But there was never any mention of the special Cosmic wheels as seen in all the adverts. Unlike Fords of the day, the Viva HB didn’t have any air extraction system. It just relied on leaking rubber seals etc so there was always wind noise and a very ineffective hot air blower. Allowing the rear pillars to act as exit holes, meant the through draught would allow far better suction on the heater system. This exit grill system was standard on MKII Cortinas and alike.

To be honest I’ve never seen any of the ‘Prince’ mods, so I fear it was a complete failure, unless a few HBs may have had a vinyl roof fitted by Crayford... So I believe the Prince conversion died a death and then Mr McMullan’s ’67 HB Viva was enticed into the Crayford workshops for a full blown roof chop. The idea of using an SL90, rather than a standard HB was that its extra power and its low ratio rear axle was more suitable to hauling the extra weight caused by all the strengthening needed to make the saloon into a useable convertible. The other criteria, which isn’t written down, but understood by most, is that all cars that were going to be converted shouldn’t be more than around 6 months old. This was to ensure the car was still in good shape before the chop.