Drilling an older 90

[scherzo]

I'm thinking of making an older 90 gallon tank into a sump.

I'd like to drill it but there are no indications of weather it is tempered or not.

It has a large (about 12") piece of glass across the centre as a brace. Instead of trying to drill the back for my return pump and have it shatter (if it is tempered). Does anyone think that if I can drill into the glass brace that the back is likely not tempered?

If I break the brace it is much cheaper to replace than the glass back piece.

Anyone with experience in doing this test?

Thanks
-Jeff