1961 Other MG Models Head gasket

My car is actually a Morris Major, built in 1931, but this category was unavailable.
The engine has been completely rebuilt but after less than 50 miles, has blown the head gasket twice. The engine runs hot and feels 'tight' on the handle, but the elec. Starter has no problems coping with it. The engine starts readily and sounds good.
I believe the problem is overheating, but how/why is there coolant in all six cylinders? Why is the gasket blowing? First time it blew between cylinders 5 and 6. The second time is unknown as the head has not been removed yet.
John Bates
Redditch, UK

updated 10/26/09
Well, thanks for the reply.

When the engine was rebuilt at a reputable engineering shop, both head and block were skimmed and pressure tested and found to be fine. The engine was rebored, and new pistons and rings fitted, etc.

Now the head has been taken off again it can be seen that the gasket has blown between cylinders 5 and 6 just as before, and there was water in each cylinder. A new, hand made gasket has been fitted and the engine still runs hot. I suspect the water pump, which is driven off the back of the dynamo (generator), and have removed it for inspection. At the moment it is resisting all attempts to open it up!

Thanks again.

updated 10-27-09

I now think I have solved my blown head gasket problem which was always accompanied by water in all cylinders and water in the sump, mixed with the oil.

The engine is overheating and having removed the water pump I think I have the culprit. With the pump full of water, I had it spinning using an electric drill (forward and reverse) and NOTHING happened. It is not pumping. All I have to do (ALL?) Is open it up and see if it can be repaired. I'm not going to be able to buy a new pump for a car made in 1931!