Minimum Radius for 2-6-0

I think your best bet is to get some flex-track and test it for yourself. For test runs you can temporarily pin the track to sheets of thick cardboard. Drill holes in a yardstick to use to lay out curves of different radius on the cardboard. I've done a lot of that with HO and N gauge equipment. You want to look for smooth low-speed operation without binding, couplers not binding on curves or any interference of other parts, and does it look acceptable to you?

This got me wondering if anyone has a rule-of-thumb formula for minimum radius based on wheelbase of the loco, although there are other factors that also dictate minimum radius.

Check the NMRA website.

NMRA minimum radius recommendations are generally arbitrary and useless if you have limited space. IMHO.

I have Gem F-3c 2-6-0's that will run at 27-8" radius.  The Wabash 2-6-0 may give different results dependent upon driver size & wheelbase.

Best suggestion has already been provided - test it out and see, and do not rely upon speculation. 

But perhaps some one with this engine will have some 1st hand information to share.........

May I suggest that your test includes loco and tender coupled to a car, as the couplers and draft gear may be the limiting items. 

ChipR

Freight cars themselves might be limiting. 2- rail cars have realistic underframes; Lionel does not.

40' and shorter cars are not a problem at that same 27" radius.  Larger cars are another story altogether.  I actually have a far tighter curve going into a siding, but that's why one has 0-4-0 switchers,

When setting up a test track to establish minimum radius make absolutely sure the right of way center line is as accurate as possible. 

When I lay out track curves with a yardstick (or whatever) drilled with holes for a nail pivot at one end and pencil holes in other places, I find it convenient to mark the track center line and the edges of the track. That makes it easy to position the track accurately, whether it's permanent or temporary.

Another way to do quick estimates of minimum radius requirements is to just draw the curves on cardboard and position the cars along it for an eyeball check. Another method (for cars) is position each wheelset on an individual piece of short track, turn them under the car and mark the angles and truck centers, then draw this out to estimate the radius or use some trigonometry if you know how. That would give you a starting point for a test track radius.

We would be interested to see the results of your tests, with photos if possible. The information  may be useful to others.