A couple of the halftracks books have mentioned that some M3A1's were rebuilt into what is basically an M3A2 configuration post war. I notice there is a second serial number on the data tag that shows a different M3 serial number that what you mentioned was on the frame. Both look like Autocar serial numbers. I wonder if 35 2 1 is a date? If that writing is Japanese I think that corresponds to Feb. 1 1960.