Something doesn't seem right here....

[TonyBagadonutz]

I'm in the begiing stages of a bath remodel...and something just doesn't look right to me. I hope someone can lend some words of wisdom, advice and caveats.

This is a second flr. bth in a SFH. The baths are located on top of each other. The plan is to swap the sink and toilet locations. The problem(to me) is that there are not enough pipes running up to/through this bath (I made this assumption based on one of Terry's drawings I have seen posted on this forum).

In the second floor bath, the toilet drain runs to a wye fitting that *appears* to also connect to the shower, and then "t"s or "y"s to the main stack. The mid point on the exposed "y" connects to a 2" cooper vent line that also serves as a drain/vent for the lav. This whole arrangement does not seem right to me.

As I am planning on swapping locations of toilet and lav., I would like to do this job right - the first time. The one thing I am relatively sure I am right about is changing the main stack from cast to PVC (at least for ease of installation).

Below is a picture of the existing piping that I feel is incorrect.
Any help would be appreciated. thanks!