There are three stamped steel door keys on T-bay right now. DF737, DF862 and DF913. These are the cost-reduced Yale keys that have the groove stamped or pressed into shape instead of brass with the machined groove.
Use these search words: antique pressed steel ford key
I spent four days walking around Hershey looking for a DF729 for my '24 coupe. The key vendors thought I was nuts, they never saw one before. They are rare.
Refer to this thread for a discussion on door locks and keys:
That key cylinder for the lock was used up until 1948 on Ford pickup trucks.
You only have to cut the extension off about 3/4th inch or so to use it in a closed car Model T.
The truck lock was my plan B if I couldn't find the correct key for my original lock. I believe the pressed steel key was only used in 1924, maybe a little into 1925.
This is a link to a 2010 Forum thread posted by Dave Sosnoski.
Best regards, John Page, Australia.
I also have a wood framed '24 Coupe that needs a key. I've done the same search through Hershey every year looking for a key for my DF940 lock but nothing yet. I'll keep your DF729 search in mind. I did check my collection for your lock but don't have one.
Most sellers don't know what they are for so I've buying them just to keep them within the T community and not in someones desk drawer or worse, the trash. If I find a key for $15 or less, I'll pick it up and as a result have a small collection of these stamped steel keys. I'm willing to pay more for my DF940 key if it ever turns up but not the other keys for $25+ currently being asked for on T-bay.
That lock can be taken apart and any key that slides in can be configured to use the lock or the lock can be configured to use the key.
No one is going to see the number on the lock when it is installed.