I think you should be fine with what you have, just take off the glass top, if you dont have the pufffer anymore.
I am using metal flashing for my reflector also, and I tacked a couple fluorescent bulb holders on the ends, and stuck two 18" actinic on the outside and have my 400W between that. You could try to stick some 18"'s in your canopy or you could go with a Power Compact lamp for actinic supp. but its not totally needed.
Also, alot of people run their actinics for like 12 hr and just have the MH's on for a 6-10hrs to simulate a dawn/midday sun/dusk. If you add corals, you will want to run your MH longer than 4hrs a day if that is the only light on the tank.

Heres a pic of my lights.

http://66.25.197.135/website/salt/light.JPG