Holley 1920 diaphram return spring

Do you think it is important that both carbs are the same number , or that they are both 1920's ? I picked up a second 3920 a few weeks back from another member , and rebuilt it , but before I asked about the throttle shaft I had already removed it to make changes so it would connect to my linkage , now have a very small leak. That 's why I was looking for another.