I looked up the GATX 30xx and 31xx series in my 1960 edition of Tank Car Capacities. Both groups had a nominal capacity of 8100 gallons and dome capacity of 171-178 gallons. This matches GATX 4121 as seen on page 28 in Ted Culotta's tank car book. That car had a 8125 gallon tank and a 172 gallon dome.

For most AC&F Type 27 8K tank cars, the"Official" nominal dome capacities, when listed in editions of Tank Car Capacities, can be 254, 256 or 266 gallons, depending on when built.

When Ted auctioned his print of GATX 4121 on Ebay, he called it an AC&F Type 27 and Ted states in his book that the smaller dome was an option on these cars.

Early Type 27 8K tank cars had 4 straps.

So, early-built AC&F Type 27 8K tanks with the optional smaller dome is what is seen in the photos (IMO).

Brian Leppert
Carson City, NV