Shower to tub drain conversion

I have a 2" pvc drain sticking out of the slab from where a 36" shower pan was in a corner. I want to install a tub in this spot, but the shower pan drain is in the wrong spot (18" from corner). My idea is to chip away the concrete and place an elbow on the 2" stub to head towards the wall, then adapt a 1 1/2" overflow/drain combo into this 1 1/2" pipe. My question is how does the tub drain hook up to all this?

You'll have to set centers of where your new drain location is and preset the piping to make one final connection.

Having open access to where that drain assembly is is a must.

drain

The way you seem to want to connect, the answer is, "It doesn't". You have to relocate the trap at the bottom of that riser pipe over to where the tub drain will be and then connect the tub to the riser out of that trap.