Is this a bowfront or something? A picture, diagram, or at least the measurements your working with would be a big help. I see others getting lost in translation including myself. It gets more confusing as you add information not originally included. You begin saying you have (2)65w already. Then later comment you want to go with the 24" because you have the VHO and 54w already? But might squeeze in another 24"?
Getting (2)24" end to end makes no sense when you can just use (1) 48" T5. Plus, by putting 2 end to end like that your losing at least 6" due to end to end endcaps anyway. Jadeguppy is correct in saying all T5's are the same width, so if you can fit a 24" in there you can fit a 36", 48", and 60.
-Justin