Okay - I've heard enough - thanks for the honest opinions.
I value all of your viewpoints - more than you know.
And I gotta say - I'm anxious to get this thing finished LOL.
I can lay this contraption on the floor, clamp a miter-box or 2 pieces of wood to each leg, and saw a straight cut across each of these six "legs". It'll take 12 fairly precise cuts.
Take out the section where the removable doors are now located.
Drill holes in each of the flat exposed mating leg surfaces - and insert a short dowel rod connecting them to each other, to keep them from shifting side-to-side. Like a wooden pin in a broken leg.
Couple screwed on vertical metal braces to each leg should keep it all snug.
Might glue - probably won't.
Will allow open back up 3 inches for incoming ventilation air, blowing warm air out the top as before. This will give me the room I need for external overflow box, and spraybars along the back of the tank/wall.
Will still have access through the front hinged door for day to day maintenance and feedings. Should be easier to lift off being shorter - for the more demanding maintenance or making inside tank changes.
Some new external 3-4 inch skirting around the bottom will insure no light escapes to the room.
Should do the trick ! Sounds like a plan. Did I miss anything ?
Saturday morning - another run to Home Depot. I can hear them now ........ "here's comes that crazy fish tank dude again" - and all the employess will scatter like rats on a sinking ship !
Thanks again y'all