I am replacing a shower in a remodeled basement in a house built in 1932. The basement appears to have been originally remodeled into an apartment in the 1950s. I removed the old metal shower and concrete shower pan to discover that the floor under the shower is the original basement dirt floor (though everything else had been tiled). The pipe is slightly off center for the pan, and before I put down a modern pan, it is clear that I will have to dig out the old iron pipe, put in PVC, and then a layer of cement on the pan floor before I can seat the new pan. (This is a standard square 32" shower base.)
I need advice on 1) digging out and cutting the iron pipe; 2) inserting PVC and sealing; 3) centering the new pipe for the pan in a way that will allow it to move a bit to seat it; and 4) how thick the concrete should be on the floor that will support the pan.