No not original. As I sad earlier, 409 car motor is 61-65. Impala SS. This W block was the first Chevy Big Block/Rat Motor. The 1958 348. That's why I thought it might be a 348 truck motor. The serial should be on a stick-out step pad on the passenger side head, in front of, and below, the valve cover.
I believe they did not use the 409 on truck. Not positive. The 348 is known to be a "truck motor", sort of.
The 348/409 was offered on all the Impalas (5) as RPO. The SS option can be 348 or 409. The 409 ran a 15 sec 1/4 mi right off the factory line. Very few SS ordered with 409 in 61. Z11. 4 different HP's. That's why you need the serial.
