Tempered glass on marineland cube

[unclebuck134]

Just bought a mint 45 gallon marineland cube. 24x24x18. It is not reef ready. I would like to drill it for a glass holes kit. How do I tell if the back panel is tempered? I would prefer not to have to use an external over flow. Any help is appreciated.

Plus I believe three sides are star fire glass. Anyway to verify? Thanks