Remove shower stall and install tub.

I currently have a 42"x60" shower stall that needs a new tile floor. It is built on a concrete slab. Since we are going to have the remove the shower pan down to the concrete slab we want to put in a whirlpool tub instead. The shower stall has a center drain. We want to install a tub with a left side drain. How is the easiest way to accomplish moving the drain from center to left. Also what is the difference between the shower drain and a tub drain. Everything is pvc, I know that the shower drain is bigger than a tub drain so I will have to have a reducer. I guess the big question is the drain location since it is on a concrete slab. I have been thinking of two appoaches. First would be to cut open the concrete floor and move the drain. The second would be to build a platform for the but to sit on and run a connecting pipe from the left side tub drain the the existing shower drain. I know I need a trap for the tub drain. I am not sure if the shower drain already has a trap (how can I tell?). Also venting, how can I tell if the current shower drain is vented? Sorry for the long post. Thank for any help anyone can give.

The shower does have a trap and vent, but it is not where you need it, so your first idea is the only proper one.

So does this mean the second option is not possible. I really dont want to have to cut open the concrete floor. We are getting a drop in tub so I already have to build a frame for the tub I figured it would not be that much more work to build a platform for it to sit on. What kind of problems can I expect if I don't move the trap and vent and just connect the tub drain to the shower drain via pvc. Thanks again for the advice. Any more help you can give it greaty appreciated.

The trap prevents any crud buildup after it from smelling up your room. If you run a long arm to the trap, any hair, oil, dead skin, etc. that may accumulate in there will reek after awhile, and it won't all wash down. You can't install a second trap, as your performance of the drain will go way down, it's against code, and if you ever needed to snake it, impossible to get a snake through. Do it right, crack some concrete, move the trap and vent where they need to be, or leave it alone as a shower the way it is!

Putting tubs on a platform is a sure sign of what plumbers call, "a Hack". aka a non-professional, jack-knife job. Yeah, it's sure is more work to do it right, but if the time ever came you wanted to sell the house, that platform would definitely be either a deal breaker or call for a hefty price reduction. You could DIY the concrete, but it can be a dirty job at best. There are professional concrete cutting companies that would make short work of cutting and removing the concrete, and there would be no dust or mess.

If the drain only needs to be moved 3 feet, the concrete could be neatly cut and removed and the whole job could be done in a DIY weekend.
Better to do it right and be proud of what you have accomplished.

My sister has a cabin in Eastern Country with a tub that has been raised. Even though I know it's raised, when I step out, I've forgotten.
Dang near broke my neck getting out.
Break out the floor, and you will be happy with the completed job. It's a forever kind of thing.
1.5" trap arm can be 42" before the vent
2.0" trap arm can be 60" before the vent.
Washing the trap arm with a toilet pulls water from the trap.