Don't put that light on a 90 gal
tank, it won't work worth a hill 'o' beans. 150w HQI won't penetrate the depth of a 90 gal
nearly at all especially with the way you have to mount those things. If you have a 4x65w hood or similar, there won't be enough room anyway.
You could get a retrofit from J&L for about 700.00- 800.00. Which would include 2x250w MH
and Icecap fans. You already have the PC
ballast so you just need to DIY a canopy. The cost of the 2x150 Coralife units would be 600.00 so I don't see its as being much of a leap.