Is it possible to install Samba 3 on CentOS 7?

1. find the centos6 SRPM for samba3 on [vault][(vault.centos.org)
2. rpm -i that source RPM on centos7
3. you now have source and a spec file, which can be used as a guide to building samba3.

But we need to both agree that a samba4 problem on centos7 is not going to be accurate replicated or confirmed by building a different version of the software and smelling whether that works.

I recommend opening a new issue - here, samba.org, or with Red Hat - and letting us know what issue you're seeing so we can address the issue. Using us like marionettes for a bit of lifting to help explore a corner case miles away from your problem means we're unable to spot and help you overcome issues that you may not be aware you have.