You can decode the block yourself, well the numbers at least. If it is an RB block, which is 413-426-440, there will be a flat pad in front of the intake on the drivers side with a few numbers. If the pad is not here then it is a "B" motor or 361-383-400, and the pad would be on the side by the distributor, cast on the block extension.
First you want to find the characters that indicate year and displacement. The year will be a letter indicating the year in front of the displacement of the motor. Since 440's came out in 1967, the correct letter for 67 would be "C", followed by the size. In your case, if the motor were alleged to be original to the car, the stamp would say D440. Your car wouldn't have come with a 440, but this example would be correct for a 1968 coded 440 motor.
Next, you will find what is the assembly date of the motor stamped on the pad.... something like 9-27 but usually not the year. You can use that number coupled with the casting date on the side of the block to determine the window of manufacture. The displacement will also be in the casting number area.
Also on the pad, you may find an "HP" stamped on there, indicating a High Performance assembly, narrowing your search to just the cars that HP motors came in, namely muscle car type models!! Since the guy told you it was supposed to be a "Magnum" motor, it should be an HP!!
Now, you may also find a maltese cross or other markings of the like indicating undersized bearings or journals or entire undersized components. There may also be WT, WR or other markings of the like indiacting a water tested block or warranty replacement.
Next, if it's a 69 or later motor, you can go to the passenger side oil pan rail area and finsd a flat pad there which may have a partial VIN, or even quite possibly the entire VIN stamped there which would be easy to identify the car wthat it came from. If there is only a partial VIN, it will give the plant of manufacture, then it would be up to you to research that plant to find out which models were procuced there to narrow your search. Without a complete VIN, you may never know but at least you can research the origin or your motor an get some of the facts!! Good luck, Geof
