Oh, yeah ... one more thing ... is current 2.7 site running https?
If so, once getting the backups to the build server with older php, don't forget to setup/open up port 443 and in this case make an exception ... set up self-signed. Can't use the certs from original server on the build server.
See ... it's true what Mr. V said ... longer one waits to upgrade, more troubles there are! :|
Give your client a virtual finger wag!
'spirit of sharing', Ken