Engine and frame numbers on any of the CBXes never match. If they are close, you are lucky, if they do match, you have a rare collector's item. Most likely all engines were produced in sequence and numbered. So were the bikes. But the engines did not get to the assembly line in order and there were complete engines taken for replacement sales and engines being held for quality reasons after the test run.
For 1979s the engine number is higher than the VIN number by anywhere between 100 and 200. I have not seen an original 79 engine in a frame with a number more than 200 higher than the VIN-number. For lower VIN-number bikes = early production, the numbers are closer together.
As Dave explained, the 1980 models had the engines numbered continuously throughout production. Beginning in Japan and ending in the USA. The VIN-numbers for U.S.-made bikes, however, were changed and the fifth didgit from the end was a "1", meaning the frames would have started with SC03-20 10 000 or SC03-20 10 001, while the first engine used in Marysville was most likely a number higher than SC03E-20 01700, which means any U.S.-built 1980 CBX has an engine serial number with the last four digits about 1,600 to 1,700 higher than the VIN-number.
1981 CBXes have a VIN number that ends with a "BC" just before the six digit "serial number" that begins with a 30. Again, engine numbers (which start with SC03E-23..) are higher, difference is typically typically less than 100 for lower VIN-numbers and slightly higher for later models.
1982 CBXes have a VIN-number ending in CC 40xxxx. Engine numbers are SC03E-24 xxxx and the numbers are usually the closest of all models. I have seen several 82s with VIN and engine number difference in the single digits.
Another long post of useless kowledge
