Shower Drain - Offset P-Trap

I'm redoing my shower and the drain will likely be directly above a joist or just on the other side of the joist from the stack/vent connection.

The existing shower uses what appears to be something like a tub drain shoe (I can't actually see it) which then extends approx 1' across the top of the joist to the p-trap. (see attached sketch)

Is it legal to have the ptrap "offset" like this?

In the new shower the drain is in a different location so the offset needed will only be a few inches although I will likely have to enlarge the notch in the top of the joist to accommodate the new 2" drain (existing is 1 1/2").

drain

If the drain is 1 1/2" it was never proper and they may have jury rigged a drain together.

The drain was installed in 1969. I'm guessing the 1 1/2" for a shower was OK back then.

Thanks Bob M

The problem is that the new drain location is close to being directly over a joist. Moving it 2" or so to get away from the joist throws off the whole layout of the bath (e.g 48" for the vanity would be 46" nonstandard) etc. Does anyone know if the "tub shoe" arrangement is "code" for a shower. It is ok for a tub where the p-trap directly under the tub overflow and not the tub drain.