For a 3x3, 300 watts of light is plenty. Go with 6 cobs @ 50w each or 4 at 100. Use a variable output driver so you can dim them. In veg, you will want less light, maybe 150 watts. Then increase it to what the plants will tolerate when you flip to flower.
It sounds like you want to retro an existing fixture? Growmau5 on youtube used to have a bunch of diy videos showing how to do that. He got banned and is back, but I don't know what he has for content.
The issue with a retro is that the blurple lights came with substandard drivers. Spend the $100 and get a good one. Don't mess around trying to save a few bucks.