It's an awesome setup!!! The rays will have plenty of elbow room.
I hate to be the one to point this out. But, you need to know for med dosing, filtration, and potential bio-loading. That tank is actually 269 gallons.
All measurements in inches: Length x Width x Height/ 231= Volume in Gallons
72 x 48 x 18 / 231= 269.298 Gallons (figure 265 by internal dimensions)
I noticed this because I have a 350 that's the same width and height but, it's 8 ft long.