There is no vin number located anywhere on the frame of a 69 impala
3RB-012812 is not a frame number for a 250 Yamaha dirt bike; it's a motor number. To find out the model year and frame, you need the frame number.
You find it as a 17 digit number stamped into the frame on the left lower frame rail.
http://www.hemmings.com/parts/search/?start=0
the frame
http://www.decodethis.com/164679U223937
Look on the frame
A Yamaha dealer should be able to help you, I don't know how to read a frame number.
Open the cylinder and look at the frame that is usually hidden by the crane. The serial number is stamped on the frame.
Look on the butt or the frame.
try the frame and butt
Kx250m001763
When you release the cylinder from the frame,you should find the serial number at the base of the frame and on the crane at the swivel.