Postwar Minimum Radius

Everything Postwar will run on 031. You may have a lot of overhang with things like the FM Trainmaster and the Hudson, but it will all run 031, including the PW #022 switches.

Thanks!  That is great news.  Back to planing.

While Art's comment is true, be aware that some large engines might have significant overhang going around O gauge curves. An example is the 773.
I had to move a number of items that were too close to the tracks when I got one and wanted to run it.

Having just completed a post war layout, and running only post war, I would offer this  advice:

Big locos - FM Trainmasters, 746 and 773 all do have significant overhang coming in and going out. Try to use at least o42 if you plan to run these.

Large engines not quite as big as those above - F3s, 726/736, 2046, 2055/6, 2065 all will run nicely but look a little big for the Curves. The 671/681s have a lot of backsplash.

I found on o31 loops the best looking stuff were small steamers - 2037, 221, 224 and similar look really nice on o31. Small team switchers - 0-4-0 look great, as do Alcos and NW Switchers. 

Passenger cars of the 2400 series variety fit o31 well and look pretty ok - 2500 series cars look absurd.

Small boxcars - 6014s and 3400 series are fine - 6464's get a little clunky.

If you can't have big curves, use equipment suited to those curves for a more pleasing look. 

I would try hard to use all 42 inch on one loop if possible.   I also have an inner loop of 31, but at least I can run most big stuff and not have it look ridiculous on the outer loop.   My table is 44inches wide, so it's at the edge, but when space is at a premium you have to do what have to do.  

I originally had a Fastrack 36? inch outer loop and everything ran pretty good on it.

I maybe should have added to the Fastrack rather than switch everything to tin track, but I had O27 on all inner track and it definitely needed replaced with O gauge track.  I replaced everything with 31 and 42.

If you already have O27 track, a nice small space option for all postwar is available by using Marx O34 curve sections. I've been using it for years instead of O31. I prefer the smaller profile of O27 rails and the radius is a bit wider than O31.

I'm on the same train as Jim above on this one.  Both the rails and ties of 027 are more realistically sized.  Marx 034 is still pretty easily available, and another nice advantage is that it features more ties per section than the usual 027 or 031.  Sounds like you may have already committed to 031 though.

Thanks for the replies! I may be changing the layout fron an island type to around the room, which would offer much larger curves.  I am still finishing it he roomalimony with stow other rooms I am working in at the same time, so it will be a while before I am ready to star building bench work.

The numbering system in an indication of weather an engine is O or O-27.  It has been explained here in the past.  The 600 and 700 series were O gauge and the 2000 series were O-27.  This falls apart when you see identical locos numbered in both series like 671 and 2020.  But is you identify the dual numbered locos and put them in the O-27 category, I think you will end up with a list of O only locos.  There is no doubt that the largest diameter curve you can use will result in both a better looking and better operating railroad.