You can see the differences pretty clearly with it assembled. There are three indications. The actual 261 carb is pretty rare.

http://devestechnet.com/Home/TheVenerable261

Middle of the page.


Deve

1950 Chevy 3100 Deluxe Cab
1950 Chevy 3100 Standard Cab
In the Stovebolt Gallery
The Think Tank
More info and tips at Deve's Technet