Hi Rob,
I think the most important thing is to avoid that the cylinders slide up, when you take off the cylinder head. They would get leaky from below and water could come into the cylinder. If a cylinder slides up, you would have to seal it.
To avoid that, you have to turn the head around 20 degrees WITHOUT LIFTING IT. That is possible, because there is a hallow shaft in the block, which helps to fit the head on the block. The hallow shaft is the center of rotation. It is in the right middle hole out of the holes, in which the cylinder head bolts come (inlet side on Renault 807 crossflow engine). I attached a picture, where you can see in which hole the hallow shaft is, but on the picture there is a crossflow head. Do you have a Federal S2 Type 65? The Federal S2 has this crossflow head. If you have the non-crossflow head, I am not sure, whether the hallow shaft is at the same position, but it would be logical.
After you removed the old gasket, you should clean the sealing face, but I think that is obvous.
When you install the new gasket, you should watch that the gasket is fixed on the right postion and that it is not able to move while you install the head again.
I'm sorry, for my quiet bad explaination, but I hope the picture helps to unterstand.