If it's from the 60s, there won't be a modern HIN, they started in the early 70s (73 I think) prior to that there was no official identification scheme. they mostly went by hull numbers. If you can get inside look around carefully it may have been documented at one time which will provide all the information you need to positively identify the boat.
Best way to determine value is to check the ads for other boats same year and make in the same condition, hopefully in the same general area, compare them to that one and base your offer on that.
No idea of values where you are, but here in michigan values fluctuate (sometimes wildly) with the seasons. A $5000 'summer' boat purchase can easily turn into a $1500 'fall' purchase because people are looking to avoid the haulout, winterize,storage fees, and potential maintenance costs.
If the owner is paying for storage, and it's being neglected, you can most likely get it at winter prices.
Ken.