No you can't mount anything but a 36" T5HO fixture unless it says it will "stretch to fit" but you don't want that.
One of those links you posted wasn't even T5HO ! It was PC lighting!
I suggested the best T5 lights earlier, ATI is the best, then TEK, Aquacatinics, Aquaticlife, Catalina, current, Hagen/fluval.
If you need the mounting legs the TEK is best, but you pay extra- check reefgeek or bulk reef supply.
Aquaticlife, catalina black solar and current nova extreme pro are the next in line..unless you experiment or buy something that isn't produced anymore..that's not all bad either. I think TEK is done now but you can find them cheap now also!
If you really want cheap I would recommend Fishneedit 4x39w T5HO. I have a 30" 4x24w fixture, they aren't great but they have a warranty, way better than Aquatraders' odysea.
Fishneedit will ship you a (return) shipping label (on their dime) if anything from the bulbs, ballasts, or a loose screw (I had that happen, check the screws) for 6 months. The bulbs that come with it are no good but after I changed them to ATI bulb ($80) its been pretty good. Way better than odysea, it has a proper warranty! Read the warranty on Aquatraders, they charge the crap out of you and you will pay for shipping cots etc.. I hope you crossed them ff your list.
You can PM me if you you want, I'll help you out.