It is exactly the opposite of moving a tub drain to a shower drain.Bust out the concrete to where you need it and hope the drain runs under it . Place the drain where you measured it to the center of the overflow and center of the tub drain out is where the shoe will be.Work backwards from the tub to the drain. Sometimes you have to take it all apart to get the tub in and lined up. Thats the fun part. Install the overflow onto the tub prior to installing and stab it on the way down. It is a lot easier this way If it doesn`t line up in the first try or two,just pull it and don`t waste any more time. You`ll have to lay down and hook it up. BE SURE TO TEST IT.
As far as issues you never know til you get to the drain pipe.