Bathroom galv/ci replacement

[Hippyies]

My antique plumbing... 1&1/2 galv pipes rotted out and destroyed the kitchen ceiling. (my next project) Tub was dated 1939. No venting back then...
The yellow rag was the sink line 7.5 feet from the stack. Toilet flange is obvious, the blury silver plug was the tub line.
The joist have been mangled & a "header" was installed.
The drywall behind the pipes is a soffit in the kitchen where i would like to move the pipes to, there is enough room to put the new 2" shower drain under the "header" ( i'll beef up the joists and header) so if i...
Support & cut the stack at the bottom of the soffit and above the existing horizontal run...

 

[Hippyies]

The soffit is 16 inches tall so i could run the toilet to its own 4x4x3" sanitary tee on the stack, a short enough run not to need a seperate vent?
Run the shower & sink to a 4x4x2" sanitary tee on top of it... 2" for the shower, 1&1/2 for the sink joining the shower line with a 2x2x1&1/2 wye?
The shower line should be borderline legal without a vent? 30x60 shower, drain hole 8&1/2" in from wall, plus the length of the trap, minus the length of the right turn to the stack.
Does the 45 degree drop into the soffit affect the measurements of the trap arm length for the shower?
The sink will need it's own vent though... Correct?
Obviously the supply lines need work too... I'm comfortable with that. This is my first real experiance with residential dwv lines, but i've done alot of drainage and drinking fountains at work...

 

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[Terry]

The picture doesn't give much to go on. Interesting framing job though.
The toilet can be wet vented by either the shower or the lav, if the locations are in the right spot for that. I don't have an idea of your layout though.
Often in old homes with very little structure in the floor joists, I prefer making the side runs below the joists and soffiting down for them. Some older homes had high ceilings anyway.
Vents can tie together at 42" above the floor.