Hi Paul. For those time frames, You should go with the MTH R1, bmt standards, Q cars, and the lo-V. The r-1 and bmts are premier sets which runs best on o54 curves (they may take 42) and the lo- v is a railking model which runs fine on o32 curves. The lo-vs can often be obtained from auction sites and the buy sell board for reasonable prices. The premier sets are a little more expensive and harder to find but they are out there as well. All are MTH and there is no word on if they will make them again, although I haven’t read about them selling the molds to these models). Lionel has never made subways from the time frame you are looking at.
I retrofitted a subway line into my 45 inch high layout. I simply added crossbeams and cut some spare base wood, keeping the whole plan simple and open. I have 3 subway stations, 4 yard spurs, and two loops under the layout with o54 curves. It wasn’t too difficult Here are a few older videos which may give you an idea ( the green engine running on the outer subway line in the second video is a premier R1).
Also, don’t forget that retrofitting an elevated line is also a fun addition. Good luck.
