You are correct, it is not a four corner idle carb. Always good to check in case a previous owner swapped blocks and drilled the body to convert it.
But the images on Holley's website show a four corner idle carb - that's Holley's mistake. Their circa 2018 catalog had it correctly described and pictured.
On the top of the metering block are additional numbers. On the older Holleys, often the carb list number will be stamped (eg 4777) other wise it will be the block number. Just another clue when figuring out what you have.
