the top is just 1x's biscuited and glues together, and then just a routered edge on the front and 2 sides... the back of the table top is flush with the back of the frame... i left my back completely open, for full access, and my whole front comes off for full access to my sump... i used 1/4" ply for the outside, with 1x3's for the trim work... simple and easy, yet nice looking... mine is sitting in the basement family room...
ummm... when i made my frame, i made it so that my tank(90 gallon) could sit right on the frame and not fall in, so my frame is 48.25"x 18.25"... then my table top overlaps the frame by like an 1" on all sides but the back(flush)... yours would be about 56" x 13.25" then... is that ok with you. or do you want more depth(like 15" or so).
then on my tank, i am only using a 20 long for a sump, so size did not matter at all for me... yours does however, so, you want only like an 1" clearance on the sides(making the inside dim 50"), or do you want wider... remember, the wider you go for inside, the wider the top will have to be... i was making it as tight as possible, therefore i choose 50"... for your height, i would go at least 10", if not 12"... is your bottom tank going to be a sump, or a habitat for fish... mine is a sump, and i have 12" clearance for maintainance. might want more if it is going to house fish, just for ease. but all up to you, i am here just to draw up what you want...
are those dimensions you gave me earlier the dim's with or without the trim... if not with trim, can you let me know what it is with the trim...