I was going to ask a similar question! I saw a truck with a 1674, so I searched to find out what a 1674 is. Similar size to 3306, but different engine.
Then someone pointed out the 1693 is the same size as 3406. Somebody remincsed about the unique sound of the 1693, including that the turbo screamed! Another poster commented that you can put that turbo on a 3406. The turbo is a Garrett T1810.