24x48x36 to a 24x48x72
Uhhhhh That is too random for me to guess. If you are just doubling the length, and its still 48" tall, then a T5 HO 6%/5.0 + a 6500k would give usable UVB for about half the cage height, if the T5's each had their own reflector.
If you are going from a 3ft tall cage to a 6ft tall cage, then i would go with again having each T5 having its own reflector. But switch to a 12%, so that you get usable to about 36", and keep the basking area at 12-18" instead of sub 10".
If it really is a 6ft tall cage, you may want to invest in some LED, as i had a hard time keeping everything lit. One thing i did do with my 7ft, was hanging the T5 in the cage about 1ft down. This had an unexpected benefit. It turns the entire top of the aluminum hood, into a 90F "heat rock". Once i found that out, i did it to all my cages. I routinely will have the cham, frilly, and beardy, sitting on the light
Im not telling you how to run your life, but a $250 UVI meter may pay for its self over the life of the cham. I could reduce my bulb changes down to every 2-3 years, vs changing yearly "because i didnt know the output".