Top tanks were changed around quite often I think, my uncle and grandad had a Diesel Fourty that was actually a Diesel Thirty Five, when it was new Valley Tractor in Modesto was renting Cats to the loggers and they sent this Diesel 35 up to the hills and the logging company turned it down and said they did not want anything smaller than a Diesel 40 so they took it back to Modesto and changed the top tank to a 40 and sent it back as a 40 ,the logging co. never figured out what they did and that old girl worked for many years as a 40 nobody ever figured it out or cared