In the event that it currently runs you could fire it up and ride it for a while . . .
That is unless its just a frame and then you could just push it around . . .
Just take it slow and take a lot of pictures. Put all the small parts, bolts, etc . . . into labeled ziplocs. But my advice is get it where it can run because a project like that could take awhile. Once its running, then start modifying.