That's the gasket between the cylinder head and the manifold 'tubes'. I'm meaning the gasket between the manifold 'tubes' and the 'box' which has the Ford Racing / Puma / FRP number cast into it.
I used a silicone instant gasket when I put mine together, went for an up to 250 degree centigrade RTV. Seems to do the trick but I should have applied a little to the inside of the heads of the bolts to stop air leaks then I would not have had to apply more around the heads. (Had to use an incense stick to find the leaks and clear a running lean fault code).