As for the LED it depends what led your talking about. A 70w light with Samsung g 301b or equal efficiency will cover 1x2ft flowering. Maybe a bit more with autos since you will get your desired DLI by having lights on 18h or more.
If I were going to grow in a pc case I would build my own light using 1ft strips if they fit.
Or some cobs.
Or what might be good is some Buddies from grow lights Australia . They are fairly cheap and they will tell you what driver to use. Plus you can stick them on the ceiling and walls of your pc case.
I wouldn't buy ready made light for this type of situation as your light will need more clearance from tops of plants
Buddies are the flexible answer to LED side-lighting, under-canopy lighting and supplementary lighting to enhance almost any existing grow light setup.