the racks you just posted would be perfect. but just need a top and bottom shelf. and it must be over 20inches wide to support widthwise 10 gallon tanks. otherwise the design for that 75 rack is perfect and i wish i had it!
So I can cut that stand up for you right? I actually have another single one just like that. None are used for fish tank these days. they are actually 20" deep (23" outside dimension).
"2 width wise 10 gallons, and a 20 lengthwise"
You are going to need a stand that is at least 49" inside dimension based on the above specs. Add another 3" to the overall length because of the 2"x4"