I always understood that all Packard built engines used the V-1650 designator code and that only when fitted to RAF aircraft were they officially called Merlins. I know Packard used locally sourced engine components/ancillaries and was also the first production to use the Wright supercharger drive on the V-1650-3 but I never knew that they built different engines for the USAF apart from the P 82 engines with opposite tractor.
The Lancaster engines confuse me the RR Mk 24 was equivalent to the Packard Mk38 with 9+ lbs boost which seems to have been replaced with the Mk 224 when 18+ lbs boost was introduced however the RR engines seem to have had either +12 or +16 lbs boost. I dont know the difference between the various XX marks which seem to have come in a bewildering variety of models and obviously need to do some research. Prop shaft differences also seem to have generated different model numbers
As to the cam boxes I came across an engine in a German museum labelled as a Packard V-1650-1 from a P40 that had RR cam boxes. Wish I had taken a photo now, I wonder if it was a Merlin mislabelled or was a genuine P40 engine that had been rebuilt with RR cam boxes.