One other option is to buy from a local auto parts store, a mechanics mirror on a telescoping rod. Jack up the rear of the car (safely supported with jack stands!), craw under the back and use the mirror with a flash light to get a peek along the top side of the tank, in the area between the top of the tank and the bottom of the car.
If you loosen the two tank strap nuts on the long studs, you may be able to pull the tanks downward an inch or so to get a better look.
It true and what I have heard also. Very few Norwood built cars had build sheet found it them, but then again, I have now idea what percentage had them but it worth the look for yours
Good luck with this treasure hunt!