I have a 638-3, pictured, and recently picked up a 638-2 (no lock), sorry no picture yet.
I love the humpback and have an older 649 and 49 as well.
I purchased the 638-3 first to serve as a back-up to my 642, in case of a mechanical issue.
I have stuck with the 642 (most recently a PC model) but now that I have the 638-2 in hand I may have to see about making a change.
The -2 is not easy to find but if you are persistent you will run across one at the right price at some point.
Now to find a decent Model 38 at a reasonable price!
