that hood is not designed for MH lights, so don't go down that road. Modifying a $600-$700 stand and lid is not something I would do, as its resale value would be nothing.
4ft t5HO lights will sit under the hood perfectly and will provide enough lighting for you to grow almost anything.
your t8's are ok at the moment, I'd recommend having at least one that is 10000K as they are not that bright.
high output (HO) tubes do not conform to the same wattage rules as the normal tubes,as you get more light for the same amount of Watts if you see what I mean.