State by state muzzleloading regs can be researched here:
http://www.cva.com/company/regs.htmThere are other issues that will preclude the use of the converted 45-70, many states don't allow 209 ignition, only standard percussion #11 or musket caps, smokeless powder is another that is prohibited in a lot of states as are sabots and jacketed bullets.
Texas law says a muzzleloader can ONLY be loaded from the muzzle, since your barrel says 45-70 right on it, that would be hard to convince a LEO it's anything but a centerfire rifle that's been converted temporarily.
Good luck with it,
Tim