Your tank works out to be 280 gallons, but a standard 240g would be better.
To me, you can get away some with the thinner tank but need length to compensate. I think a 80" x 25" x31" tank has a footprint bit on the small size for a large aro. With the 240g demensions I think most were assuming (96" x 24" x 24") you are OK with having an silver aro until it's about 30" long. To grow that large could take anywhere between 5-12 years, although there are cases of silvers reaching 3' in 5 years.
To me, you can get away some with the thinner tank but need length to compensate. I think a 80" x 25" x31" tank has a footprint bit on the small size for a large aro. With the 240g demensions I think most were assuming (96" x 24" x 24") you are OK with having an silver aro until it's about 30" long. To grow that large could take anywhere between 5-12 years, although there are cases of silvers reaching 3' in 5 years.