As I read all these post and most all the suggestions are very good and need to be fixed, but they basically direct the problem out the overflow tube and do not address the root cause. If it overheats under load and it overflows out the cap and onto the hood, you have a blockage at the very rear of the block in the water passage directly around number 4 cylinder. This is very common with model A's. That water passage is only about 1/2" wide by 2" tall at the very back of the block and the A engine sits at rearward tilt. This passage can easily become blocked and most engine rebuilders do not take the time to be sure this passage is open. When a Model A sits over a period of time, the cooling sediment can settle in this passageway. The Model A cooling system will cool the A just fine, but if that rear passage is blocked, it will turn the cooling water to steam under load and this will push the cooler water out through the top of the head and over the hood.
To fix the problem, the head needs to be removed. I like to take a 1' section of hanger wire, hook up to a battery powered drill and snake it around the back of #4. Thoroughly flush it out while you are spinning the wire. When you think you did a good job, do it again. When you are finished and your ready to refill the car with coolant, add a spoonful of anti-foam powder. This can be purchased at any hardware store that sells rug-cleaning supplies; it is used to stop foaming in carpet cleaners. This will work great if your water pH is not correct.
Now if you still have a foaming issue in just the water and it's not pushing out over the hood under load, you have a compression leak; either a bad head gasket or cracked block.
