Thanks for your comments and thoughts Anon, taking into account what you said this evening I looked at the Pratt and Whitney R-1340 which appears to have very similar cylinders. Then I came across the BMW 132 engine which was built by the German’s under licence from Pratt and Whitney, this engine appears to have the wire clips fitted for the rocker covers. A quick check on Wikipedia shows that the BMW 132 engine was fitted to the Junkers W34hi and this version was mostly used by the Luftwaffe to train pilots and radio operators which fits nicely with the use of this airfield. At the time of of acquiring this item it did come with some other W34 items but there was no provenance to the engine cylinder other than the airfield it came from.