You can use the R12.7 variant for PoC. It'll work for PoC. But do not suggest using the same for PROD unless certified by GD. I'd do that to get a head start, but with the caveat.
I don't know if there is a BETA version available. You can reach out to the CA Account Manager, who could then check with Product Management (Engineering), if there is a BETA build in pipeline. The way certification would work is CA would pick 6.2 and run it against R12.8; then update code in 6.2 if need be.
| For PS R12.7 on Windows 2012 R2 x64 | ZIP | 871 KB | 6.2 |
| For PS R12.7 on RHEL 6 x64 and RHEL 7 x64 | ZIP | 1.3 MB | 6.2 |