Not necessarily. My 1979 model has different numbers for the frame and engine. The Haynes manual for the DOHC models (1979-1982) has a listing of the ranges of numbers for frames and engines for each model year. Perhaps the same exists for the SOHC models?
I'm also remembering a website that has that information as well, collected from various riders over the years. Maybe a Google search will find it?
Good luck, and post a few pictures of your bike. We'd love to see it.
Luke M
Used to have a 1979 CB750L, sold it as a parts bike, now riding a slightly modified 1984 VT700C. Network/Field Engineer. Central OH, USA, Earth, Sol System, Milky Way Galaxy, Universe.