the way i planned mine was to have the 29gallon appear to be just a glass panel below the 75gallon tank, none of the black is shown, and the glass is nearly flush with the front.
with a bowfront tank, that won't be possible.
I'm not sure of the dimensions of a 72bowfront vs a 125, but if the 125 is much deeper, you could just build the stand deep enough for the 125, and then the outermost point of your 125 can be flush with the front of your stand, and the rest of it could be set back in your stand a little.
I think the whole thing would work much better with a flat front tank really.
unless you want to nearly steal my design, and have access to a jigsaw.
cause here's an idea, have the back and side walls of your stand flat, but then cut the top for your stand to a size that will fit the 125gal tank, but then in the front of it, you'll have to have it come out in the style of the bowfront tank. then you can use 1x6" like i did, so you won't really have to bend any wood, and make the entire front of the stand bowed in the same way as your 72gal tank?
make sense?
i'll draw a quick sketch then upload it here