The Stratocruiser engine (per FAA type certificate E-247) was the P&W Wasp Major. The military equivalent was the R-4360, and it was the US military that imposed the uniform R-, O-, V- etc. numbering system. The number assigned is the CID rounded off to the nearest 5.
And yes, two completely different engines could wind up with the same designation. There was a Curtiss V-1650 of 600 HP in the 30s, and the famous Rolls V-1650 of double that HP (built by Packard in the US) in WWII.
(I once helped assemble the former for a museum aircraft.)