Meaning, the SE has significantly more robust power supply than the Plus and can therefore endure more heat. However, the Plus does NOT have a hard drive. The full height drives used in the SE FDHD would significantly increase the heat in the case, well over that inside a Plus, as well as block a lot of the front vents in the SE which might otherwise provide reasonable ventilation.
If you were to remove the hard drive and run the SE for a limited amount of time between cool-downs, in an adequately air-conditioned room away from other heat sources, like lamps and external hard drives, and ensure good air-flow around unobstructed vents, it might be safe to run the SE this way. However, it would most certainly increase the strain on the components and thus shorten their life.