Those flanges are what hold the top and bottom pieces of the tank together.
I could do it for you on one of my spare tanks. I'd cut the flanges off, weld the tank pieces together really nice, do all the filler and paint work, seal the inside and re-paint it for you any color you want! I'm busy right now so for a rush job, I'd estimate around $400 for labor and materials, I'll throw the tank in for free!