Those Honda 400’s were great bikes in their day, I knew a few guys that had them. If you absolutely had to have one now to recapture your youth, I would say that an absolutely pristine, low mileage bike like that (original paint, under 10,000km.) would be worth $10,000 to many of the the right people. You would have a hard time restoring one for that amount of money even if you got the bike for free. There’s nothing like pulling into a local bike night on a mint original bike like that where GSXR’s are a dime a dozen. There was a guy that use to attend bike night at Haugen’s just outside of Port Perry on a ‘72 Kawasaki H2 with a nice “patina”( it was actually a little beat up IMO). He was like a rock star every Thursday night when he pulled into that parking lot.