A lot of plumbing from 1931 has changed for the better.
We know that that the S trap was not a good idea.
We know run 2" pipe to the santee and then a 1.5" trap arm.
The vent can be 1.5" too.
There should be a 2" cleanout on the line too.
If you cap off the previous line, it doesn't matter much where you cap it.