window lock

Hello - I've ordered (and got it) a part #90-298 (Flush Mount Lock, 1-5/8). The size is exactly what I need. But there is a little but very important difference between 90-298 and the lock I have. My original lock doesn't have "walls" (for the lack of the better word) that go around the part on the back. If you take 90-298 and compare it to the picture I've uploaded, you will see exactly what I mean. My original lock "slides" into the window.  Do you think you can find what I am looking for? I wiil need 15-20 of those (on the picture you can see a serial number, hopefully, that helps.). Please, let me know.
Thank you,
 
George