Sadly the
"Mini Traveller and Countryman Register" website is no more....however much of the previous website info can still be found archived via the
"Internet Archive - Wayback Machine" and searching for:-
minitravellerandcountrymanregister.org
A quick search on there found this info below which might help but no exact mention of the flat to fluted sills:-
March 1960
"The rear floor pressing of the early estates resembled that of an extended saloon, with the battery being retained in its traditional Mini location in the boot. One of the most interesting things about the very early Traveller and Countryman cars was the internal fuel tank. The tank was positioned on the left hand side in the rear of the car and was trimmed to match the boot. These so-called internal tank cars are easily recognisable by the filler cap being just underneath the rear window on the left hand side of the car. Production of the internal tank cars was so limited that these have become the most sought after of all Mini estates.
September 1960 also saw the first production change to the model as drip rails were added above the front doors.
One month after launch the second production change was implemented as the estate cars, like the saloons, started to be fitted with recessed screens.
April 1961 the all-steel estate was launched for the overseas market only. The first recorded all-steel car was a Morris Mini Traveller with chassis number M-AW4-85867 built on 7th February 1961. It was Cherry Red in colour and was despatched on 16th March 1961 with the destination recorded simply as "Europe"!
October 1961
From internal to external tank.
12 months after the estate launch there was a major change to the model, as it adopted the van-style fuel tank located underneath the car. From here on we refer to "external tank" cars. Consequently the filler cap moved to the moved to the lower right hand side of the car and the boot floor pressing was revised. The battery was moved from the boot to underneath the rear seat, on the right hand side.
January 1962 the Austin Se7en Countryman, like the Austin Se7en saloon, adopted the Mini name and became known as the Austin Mini Countryman, beginning with chassis number A-AW7-197104. The rear door badges were altered to reflect this change.
At this time larger brake cylinders were fitted to all models and a plastic oil filler cap was fitted to the engine.
October 1962 All-steel version available in the UK and more changes.
The all steel estate was made available for the UK market with the first all steel Morris Traveller being an Almond Green car with Grey & Green interior, having chassis number M-AW4-308939 and body number 28724. This car was built on 2nd October 1962 and despatched on 9th October 1962 to Haslemere in Guildford.
The first UK all steel Austin Countryman was a Smoke Grey car with Grey interior and chassis number A-AW7-304947. This car was built on 25th September 1962 and was originally destined for the export market but was transferred from export to home sales and despatched on 9th October 1962 to Saunders in Hereford.
Costing £605 6s 6d the all steel estate was 22 pounds cheaper than the "Woody" which cost £627 6s 6d.
At this time synchromesh was fitted on the top 3 gears and the fresh air heater/demister was fitted as standard, replacing the recirculatory type.
September 1964
Yet more changes!
In line with the saloon, various changes were made to the Mini estate in September 1964. These included:
Ignition key start
Black speedo in oval cowling
Oil pressure warning light in speedo
Sun visors added
Rear view mirror now standard
Modified gearbox
Automatic gearbox and ridged roof appear.
In
October 1965 an automatic gearbox was made available for the saloon and the Countryman/Traveller. Known as the "his & hers" system the automatic cars could be driven as a manual or put into fully automatic, letting the car change gear itself.
Also at around this time the flat roof of the vans and estates was replaced with a ridged roof, which eliminated vibration and noise.
October 1967
Launch of the Mk2 and Mk1 Traveller discontinued.
"Mini Traveller and Countryman Register" as seen on the "Internet Archive Wayback Machine."