Is this a 489?

The foundry that cast the case did not just ‘leave the 9 off’.
The number 9 fell off the mold and they continued to use it that way. The characters that make up the part number are individual numbers that are typically silver soldered to the pattern. Do a lousy job soldering them on and they fall off while in use. At the International Harvester foundry that I worked at ,long ago, when that happened it was required that the missing character be engraved into the casting as having the correct part number on the casting was a part print requirement.