I think the instructions you found look reasonable and can be adapted for 7.3. Don't do an "--enablerepo=*". It will probably fail and is dangerous if it succeeds. Better may be:

yum install gcc kernel-headers kernel-devel

and if one of them does not install, try a "yum search package_name --show-duplicates --enablerepo=*" (which also may fail if some of the repo URL's of the disabled repos fail. Installing VirtualBox by yum is the same. Just enable the repo you need.

You should be able to cross-refer to any Centos7 instructions as well like this.

If you get it going, fell free to post how you did it.