This is a jimmied-up list of what ground and sea vehicle companies that I would believe would have existed in Crimson Skies, taking what I can see from the old Crimson Skies Universe Corporations page.
From what I can see, the major car/truck manufactures at the time were Ford (as in the Ford Hoplite), Rolls Royce (who make most of the engines in the game), and the Canadian Car & Foundry (look up Bell Aviation on the Crimson Skies Universe Corporations page). These companies did exist in reality, but their designs in CS are different. Chevrolet didn't exist for some reason, but if anyone finds proof otherwise, I can change that.
Ford: as explained above, they build the Ford Hoplite, or autogyro, which means that Imperial Taxi and others would have big enough contracts with them that they would have enough money left over to produce ground vehicles and still make profit in an aerially dominated world. These vehicles would commonly be civilian, such as small coups and pickups on Model A frames, and larger trucks, which were generally the front end of a Model A, with an elongated rear end.
Rolls Royce: for some reason makes the most powerful engines of the time, commonly used on zeppelins. Again, leaving enough profit to build ground vehicles. As they do today, Rolls Royce would be more for luxury, like the limos of their time. There can be multiple models, but all are more centered to the luxury of the high life.
Canadian Car & Foundry (CCF): part of the Bell Aircraft Corporation, the CCF is more centered around Mass Transit, by building busses and railcars. They don't build any small cars, but make just a good a profit contracting part of their factories and facilities for Bell to make Valiants. They also seem to be part of the General Motors/Messerschmitt company due to some sort of lawsuit, but too many politics to explain.
Trains: train companies are at the dwindling end of the line. The only company that would exist is Pacific Locomotive Company, but the game doesn't really explain the railroad business as deeply as one would hope. All I do know, is that there where the usual freight trains...
And the COOLEST looking passenger/express trains...
The major personal boat builder at the time was Chris-Craft Boat Company. As for who builds the gun boats, I don't know. Military boats where often built in government shipyards, but since there are so many governments, and only one kind of gunboat, I can't say which one built them. So for know, we'll leave them alone. Larger ships where built by Peninsular and Oriental Steam Navigation Company (P&O). Submarines (such as the one in the last Hawaiian mission in the game) also fall into the "government- built" category. But there is proof that Japan had aircraft launching subs at the time. But considering the one in the game was British-owned, we have a good idea of where they are based. Yachts were built by the Mathis Yacht Building Company.
Chris-Craft Boat Company: the only major personal watercraft building company at the time. These boats were very expensive, but very fast for their time.
P&O: most ships at this time ran on steam and coal, at least until the late 40s. The Red Cross medical ship in the game that was based along the cliffs was common as a P&O passenger liner, and the Russian oil tanker you steal fuel from near the islands, and freighter you blow up in Manhattan are classic cargo vessels of the time.
Mathis Yacht Building Company: the major yacht building company of the time. Built both sailing and powered yachts.
Government/Military: I have no idea what companies would build military ships, such as aircraft carriers, battle ships, submarines, and gunboats. Possibly a sea-side nation big and powerful enough to have a shipyard (such as the Empire State, Nation of Hollywood, Confederation of Dixie, maybe even the United States of Mexico, etc.). It's best just to leave these ships alone, and let each nation build them as they please.
Please, feel free to correct me, and insert any suggestions you might have.