My boyfriend has the same medium-low tank that I am helping him set up for a ball we're getting on the 25th. I ordered two 8.5" Flukers brand porcelain socket clamp lamps w/ combined lamp dimmer switch, each for 13.48 on amazon prime. Those sized lamps should fit easily within the quadrants, and like you we are using them to maintain ambient temps during the day and night with the bulbs on a 12/12 timer switch. I haven't gotten everything in yet to experiment with temps and once I do that I will decide if I need lamp stands, but honestly with how much snakes like to push against the screen tops of their enclosures, I feel more comfortable having them on stands just for safety reasons. I ordered 75watt bulbs (zilla blue daylight incandescent and flukers black nighttime) to go with the lamps and plan to tweak the heat output with the built-in dimmer switches that come on both lamps.
With your setup, I would get a lamp stand (does your lamp have a clamp?) and some higher wattage bulbs, just to avoid melting the plastic cross beams or burning your snake.