I find cutting old glass is hopelessly hit and miss, and mostly miss at that. Only ever gotten a predictable break line when the glass was perfectly (and I mean PERFECTLY) clean.
If it were me, I'd replace the bottom panel and adjust the stand size. I hate cutting glass. Dez has a golden horseshoe up his rear (sorry man but it's true) and things just "work" for him, if you're like me and basically on the complete other end of the luck spectrum, my suggestion is don't waste your time, you could wind up losing the whole tank.
Good luck whatever you decide, and have fun with it.
