@Danny42C
Merlins came in many flavours - Derby, Hillington, Halewood, and the Packards. In my time as a graduate apprentice at Hillington we were still repairing them and developing them. I designed and tested roller rocker gear to get over the camshaft wear problem which limited the overhaul life. Never went into production though - too late. Just for fun, one day we decided to see if the supercharger off a Packard would fit one of our UK engines. Two dowels located it, and wonder of wonders we offered up the supercharger to the engine and the dowels went perfectly into the holes. Mind you I think R-R sent a complete set of jigs and fixtures to the USA to be used as templates.
When production ceased, the Americans shipped hundreds of engines to Hillington which sat in their packing cases in the car park. The bosses decided to scrap the engines but sell off the empty cases (made a good garden shed). One of my colleagues bought one (ten bob if I remember rightly) but when he opened it there was a Packard Merlin still inside! - red faces all round. Wonder what that would be worth today.