Will work on smaller tanks. putting 2 55 together mean taken one of the side glass off and using silicone to hold them together. One way or another the middle will leak, you can duck tape it and will still leak.
Try this idea
take all the glass off and just use the bigger size.
Your tank foot print should be
48" L x 24" W x 21" H
2 48"x12 = 48x24
you will end up cutting one 48x12 in half for the 2 side.
Silicone the 2 bottom glass will be fine and leak save if only the flood or stand is flat must be 100% flat
Use left over glass to build smaller tank or use it to make a glass top