Need scraper ID help

A friend of mine has this scraper located in central California. The model and serial number plates are missing. It appears to be ready to go to work as the gearboxes seem to be functional. Sorry, I did not measure the blade but it must be 9 to 10 feet long. Were rubber tires an option on this model? Any thoughts on the value would be appreciated. Thanks for your help.

There is a link inside this old thread to Chrisco's web page on CAT graders.
http://www.acmoc.org/bb/showthread.php?15260-1930-s-Cat-pull-type-grader

my guess is a model 35
use the spec below to double check your machine to confirm model.

Caterpillar Model 35
4A1 to 4A-1663 (H.C.S.F.) 7100 lbs. Built Starting in 1930

10' blade
20 3/4" blade width
9/16" thick
Frame 7" channel
Rear wheels 40" dia.
Front wheels 32" dia.
http://www.chriscomachinery.com/PullGraders.htm
and yes rubber wheels was a factory option