Insurance woes after hit and run

[mrtoni]

So i posted a thread in blazer forum about a hit and run on my 72 k5. I found the offender and filed a claim. His insurance balked as he never contacted them. Lo and behold a week later he confesses and Allstate says they accept liability.
Their adjusted shows up, nice kid. Says fixable, needs a bumper. Well, his little Cruze pushed me 20 feet, displaced axel, rear quarter gone, tailgate etc. lots o damage.
I had preprinted lots of comp sales of eBay. Not the 50-60k ones but real comps that were from about 8000-25000 for a nonrusty 1972 blazer.

I get her report today and they valued it at 8200 so if repairs run 65% of that it's totaled. I picked my shop but they're expensive silo I say no chance it'll be less than $5000. She said I cannot challenge the value, it's a third party computer program that looks at dealer sales in last 6 months within 150 miles.
I have only liability so my insurance isn't involved. Ideas?