Yep, the bigger carb, even with the offset intake manifold, will hit the tank. There are a couple of alternatives for you:
1. Move the tank back 1" and raise it 1", and then replace the petcock with one with a 90 degree outlet to the back. TrailBikes has one on their website
HERE.
2. Pick up a 12-way adapter that allows you to rotate the carb and manifold out 90 degrees to the engine, like
THIS ONE.
I have a '77 Z50A that I use as an R&D test bike for engine builds, to break them in and run them. It has both 6V and 12V electricals on it, so I can test either points-type engines or CDI-type engines. The tank is raised up and back 1", as shown
HERE, to give you an idea. I also made "L" brackets for the seat, to move it back 1".