Basement shower

[dgheyl]

My son and I want to install a shower in his basement. The shower will be about 10' from the 3" main cast iron stack (This is an older house and not the usual 4" cast iron). Right next to the main stack is an existing toilet. The floor is a concrete slab. The question is... how far below the floor is the toilet connected into the stack? Is there enough room to cut off the cast iron stack, install a PVC Tee (2") for the shower, and have enough slope to run 10' to the shower drain? Is there an easier way to tap into the cast iron than cutting it off and replacing a section?

Thanks,

Dave