Pleased you have got your money back.
Regarding the gasket for an alloy head, if you are referring to a Supaloy head, in an old price list of theirs (Super Accessories), a special shape gasket is listed for these heads. However I think your best bet is to contact Tony Leslie at Holmesdale Sevens who should be able to advise you on this matter. I suspect the only choice you will get is the high compression head Seven gasket.
As for the casting number I expect that is just what it is. It doesn't seem to relate to a part number.
Is there any reason why you are going down the alloy head route? If you are using an older 2 bearing engine it is common practice to use a later high compression head which will also let you use 14mm plugs. Sadly they aren't as cheap and plentiful as the low comp head but are available along with the correct gaskets.
I gather the "9E1" head is the Austin Nippy cylinder head so is a sports type head from Austin.
I have a new one from Tony at County Sevens in Leicester on my special. He has a supply of them available either cast in Ally or Cast Iron. The Nippy head has the plugs where they should be .... over the valves and not smack in the middle of the cylinder where at full compression there is little gas to ignite as it has been squashed to the valve side combustion chamber which is where the cooking A7 head has them ... I think the compression ratio is a bit higher and the engine is much more responsive on a 1 1/8" SU and a new Volkswagen ditributor from Mr Barlow in Nottingham. So if you have an original one look after it !! you can check if it is a cooking or sports one by where the plugs are as above. Why not use 18mm plugs on your recoiled head ? NGK do modern plugs with a bigger threaded base I have them on my 9E1 head and they work fine for the miniscule power output of an A7.
I was told that an Ally head on a standard A7 engine is a waste of time as they dont get hot enough in normal road running to make any difference to performance... they are intended to dissipate the heat faster so they can make the combustion chamber cooler and lose power rather than generating more. They are good with a tuned engine with twin carbs tube manifolds and high lift sports cam.