As far as i know its the real deal
however i didn't buy it in 1977 from a Suzuki dealer so
??
I bought it off ebay about 10 yrs ago from the US .
But i have welded a new cradle from a C model into a B frame as the B one was rotted out . The C frame had a badly bent steering head and backbone so became a donor frame .
I suppose technically it is now not eligible for pre 78
i couldn't say what year the mig wire was made that was used to fuse the two pieces
could be it has to go into pre 2010