Would it be ok to combine lighting?

You would be shy wattage I think. for FOWLR you will be OK, but Coral are in your future, you want at least 3w x gal @ 150w, the three you show ends up at 108 w.

Do you still have the glass inserts on ? May want them off anyway for the heat and air tranfer. My .02.

36" light should fit in a canopy for a 36" tank. Did you messure twice ? I just checked the inside of my canopy and the way it sits I do not lose any width. I'm sure they are all different though.

 

Shy wattage for sure. You need at least 150.
How about something like this ?
How about something like this ?
30? SunPod 1x250W HQI Fixture by Current USA* - AquaCave

Or even the T5 version

 

I was really trying to avoid the MH due to having to get a chiller.

 

Then get a different t5 ho fixture. You will be wasting your money. I promise

 

3ft IceCap T5 4-Lamp Complete Retrofit Kit (with ballast and reflectors) (For T5 )
Here's what you need guy. You go with something like this you aren't going to need a 6 bulb set up and it's way nicer than those coralife things