Thanks for the feedback on the quality of the Sun Star models as I may invest in one.
However, the filler cap is correct for the early internal tank Traveller/Countrymans:
"In September 1960, BMC launched the Austin and Morris estate car versions of the Mini saloons, based on the floorpan of the Mini van. However, like the saloon, the fuel tank was situated on the near-side of the boot behind a trim panel and the spare wheel and battery were placed under a hinged floor panel. (Later, the tank would be put under the floor like the van, and the spare and battery would be re-positioned.)"
I am currently helping my brother to restore the 1961 Traveller shown below with this early feature.
Before as found:
After with original woodwork:
Rare Internal petrol tank:
Early rear floor:
