The Lelystad text describes the installation of Beech 18 cowls in the 60s. I examined many of the above shots to determine if they had later reverted to the original Lockheed cowls - Lockheed's securing method was a "belly band" cable in a groove around the circumference of the cowl.

But the Duxford shots include an engine semi-closeup where Beech style cowl latches are clearly seen.