Choke measurements

I just got a Montgomery Ward Western Field, and the barrels are not marked with guage, length, or chokes. I want to measure the chokes, but the nearest gunsmith is a 40 minute drive and only open 3 days a week. The gun is a 12 guage, and it is 80 years old so its a 2-3/4 inch chamber I would imagine. I want to measure the chokes. If I just measure the end of the barrels will it be close enough to tell? All I have is a dial caliper. I just want to know so I know what my options are for non-toxic shot, as this is what all the ranges near me require, steel being the cheapest and not good for full chokes. I would also like to take it out to the duck blind once or twice.
I searched old posts and found the dimensions of what it should be, I want to know if measuring the end of the barrels will be accurate enough to know.
Thanks

Theres no way a dime is going in either barrel. We already tried. 32 inch tubes with full chokes, wow. Well no steel through there anyways. The tree huggers got lead outlawed at my local ranges, and I would like to use the gun duck hunting just for nostalgia. I think the long barrels (and the weight of 2) will help me with my swing. I will probably change the gun to be able to shoot steel at some point though, my gunsmithing classes start next month, and I'm sure we'll go over it.

This gun has fixed chokes, I haven't gotten around to measuring them yet.

I've seen screw in chokes that became fixed chokes, its not fun. If I do anything after duck hunting, I oil the choke threads on my 870. The gun sits in the rain all day, the stock swelled, its starting to crack, I don't clean it, Sometimes I lean it up against the wall with the barrel pointing down to drain the water, but those choke threads are oiled after every trip.