Oh blimey mate sometimes its either simple or complex. Its got new gaskets on there, just putting it all back together.Just something to look for years ago I had a SD1 Rover with straight 6 engine which started squealing on gear changes and at certain position of throttle. Changed clutch ,thrust bearings plus other related bearings. Turned out to be blown gasket on inlet manifold sucking air, hence the whistle. Just a thought. Cost £1 for new gasket
How are you recovering from your operation by the way?