[racer]

You are better off having it appraised by a local appraiser, perhaps someone your INS co can suggest.

imho, a modified '75S targa should be worth less than an original example. I imagine the 75-77 year S targas are $9-15K.. unless extremely low miles and excellent shape which then they could be $20K cars, but no one pays that much for mid-years.

Also remember that, most likely, your insurance will rise since you are looking to pay for a "stated value" vs a book value should something happen.