I've got more or less the same thing. 72.125"x36.125" on mine, and I would design your stand to allow for at least a 1/8" variance (I've had my eyes on at least 4 different tanks, and none of them were the same). The glass itself is indeed only 71"x35". By my calculations, the interior tank volume is a lot closer to 250 gallons over 300, but it's still a nice and extremely cost effective solution compared to the alternatives.