How to Remove a Stuck or Broken Model T Head Stud
One of the topics that come up repeatedly on the T club forums is "How do I remove a broken head bolt".
A picture is worth a thousand words, so I took some for you:
Watch the Welding Method
See the washer-and-nut welding method used to remove a stuck or broken Model T engine bolt.

With the head removed, you can see the offending part. This engine has obviously been sitting for a long long time, making the problem worse to deal with. It looks like the previous owner gave up.

Clean with a wire brush

Lay a washer over the broken bolt. This one is 1/2"

I chose to mig weld this, because it's quick and even an amateur like me can get decent results. A stick welder, or even "brass and gas" will work.

After welding the washer to the stump, weld a nut to the washer.

Now you have something to grab onto. I turned this one while everything was still hot. I don't think letting it cool off would have had any negative effect on the results.

Now, why does this work? Your heating the stud. Metal shrinks when it cools. So - while you were looking for the nut, lining it up, and getting your welding helmet back on - the stud cooled, shrank a tiny bit, and the rust/metal bond broke. You can see in this last photo the color change on the stud, which shows just how far in that heat went.
I will confess here that this one was particularly stubborn. What you don't see is the first try I made, where the nut and washer snapped off clean and I had to start over. If you have the same problem, keep at it and you will win eventually.