That's a tough one Leo :clonk:
My personal opinion would be a regular Beaumont, which your example seems to be, would be valued under a relative Chevelle. However, I would also say a unique or high horse Beaumont could be worth more. Of course, the market of possible interested buyers is much smaller. Example, my friend down the road earlier this year sold his 67 SD-396 L35 ragtop for probably a little more than a comparable SS-396 might sell for. The car was correct and an absolute knockout though.
I don't have any problem saying this 65 Beaumont is probably worth the $8K if it's in decent shape. In my opinion the 454 doesn't hurt its value either since it probably started life as a small block.
My concern in your proposed transaction is the fact you have not inspected the car in person. Pictures NEVER tell the entire story. I would be inclined to get a professional appraiser inspect the car for you and provide a detailed report. At least then you would have a better indication as to quality. Make sure you pick the appraiser and not the seller. This could be a couple of hundred dollars well spent.
Hope this helps a bit. Good luck Leo.