49897301830 is the complete engine number.
498973 is the part number of the engine.
That part number corresponds to a B23E engine, in a 240 of year model 1979 to 1984, which can be found in the spare parts book.
Beware of online 'VIN decoders' - they often tell enormous porkies.
The VIN plates on those cars look like this:
The section indicated in [2] is the actual chassis number; the complete sequence of numbers in that box is used as the VIN - Volvo changed the way they did VINs a number of times, and US/Canadian market cars used a different VIN system to everywhere else. As most English language VIN decoders are US-based, this is why they often tell whoppers with Volvo ID numbers.
Edited to add:
The letters in the examples above (the 'B' in 1981+; the 'A' in the 1980; and the 'L' in 1979 version) indicate the model year.