Yeah, Rover were still making them into the sixties, possibly the seventies...
The Landrover engine and their sedan range had the F-head. Rolls-Royce too, their six that was supplanted in their sedan range in 1955 by the V8 was an F-head, but it continued in production even though their cars had gone to V8 ohv.
The engines kept going in 4-cylinder and 6-cylinder form, possibly even straight 8s, in military use (Austin Champ 4WD military version, for instance) and the 6-cylinder 4-litre engine was used by Austin in their Van Den Plas Princess R from about 1964 to about 1970.
This led to the prospect of it being used in Austin-Healeys and six prototypes were laid down. Compared to the Austin-Healey 3000, the Austin-Healey 4000 was 6" wider (bodies cut up the centre and 6" added in, same with chassis), they had an improved front suspension and a Salisbury rear axle.
But Donald Healey had more in mind. They built and began testing (I believe) a full ohv head for this all-alloy engine, supposedly getting very good power out of it before the project was canned. By then three of the prototypes had been completed and they were sold off, the remaining ones were also sold and completed by private owners. So there are six Austin-Healey 4000s around the world with F-head alloy 4-litre sixes in them.
If it's of interest, the reason they were canned was because of the Leyland-BMC merger... which put 6-cylinder sports cars from Jaguar (E-type), Triumph (TR5, GT6) and MG (the unloved MG C which had an engine based on the Healey 3000 unit) under the one roof.
