I decided I really wanted a '78 RC500, but soon found that there was no way to buy one, so had to make one, and even that was a costly, time consuming, head f$#k. I know one of the real ones resides in Australia, but believe there was only ever two '78's made by Honda. I also have never seen a photo of an RC with the model designation on the seat. I doubt it's the real thing (I hope for you it is), and if it is I don't think $50k would come close. A photo is needed for sure.
Cheers,
K