I'd probably break up the concrete and see the depth of the existing p-trap if you can't determine that without. FWIW, while you can get a shower pan with an offset drain, most people much prefer the optics of having it centered. If you're going to leave it at the end, a linear drain (expensive) is a nice upgrade. If you do break up the concrete, you could upgrade that line to a 2" one (it may be under the slab). The bigger potential gotcha is if the p-trap isn't deep enough to allow the slope required to move the p-trap. While some places seem to allow a shower without a liner, or to not have the liner sloped to the drain, don't get caught in that situation. There are lots of ways to build a reliable tiled shower, but while not difficult, it is very detail oriented. Mess up one aspect, and it can fail. Much cheaper to do it right the first time. Read Tiling 101 in the tutorial section for a short intro.
If you're going to do tiling, check out
www.johnbridge.com for help with that.