Here's a picture if a rack I built for some breeder 30 gallon tanks. It was one of my first breeder racks. I've built them for small 20 gallon tanks, the largest rack stacked two 125 gallon tanks. The 30 rack worked but here are some of its problems.
1.The bottom tank is too low, it was hard to do a gravel clean and was difficult to see the fish. I never really used to bottom tank very much.
2.The tanks were too close together which made catching fish hard to do, and I cut down my gravel cleaner to fit the tanks and stand.
Sorry no plans for the stands.
I ended up taking that stand apart...with a 4 lb sledge hammer and made another stand that holds two 30 breeder tanks. That stand the bottom tanks is 16" off the floor and there is more room between the tanks. This stand is built from 2x3 that have been trimmed down.
What are the dimensions of you 60 gallon tanks? are they glass or plexi? Its makes a difference on how you will build your rack. Glass tanks can be supported at just the front and rear, plexi tanks need to be supported on all 4 sides and should be supported across the middle.
The tank on the green stand is a 50 gallon tank with Xystichromis phytophagus Lake Kanyaboli 'Christmas Fulu'