I'm running LA short block with magnum heads and intake. I used Felpro LA head gaskets #Q8553PT. I did block off the oil passages at the top of the block, but this shouldn't be a problem for you with your magnum block.
My understanding is the Magnum head gaskets have extra material to hold the pushrods in place during engine assembly. A stick or piece of wire set against the cylinder head rocker arm studs serves the same purpose.
The magnum intake ports are a different shape than the earlier LA ports, so I used magnum intake manifold gasket set with the cork end seals.
I tried the Felpro Q1008 head gaskets. They have pre-flattened combusition chamber sealing wire, supposed to be better for aluminum heads. But the gasket material was not very compressible, was a very hard material. Ended up with water leaking out of both head gaskets. No, I did not coat them with a spray on sealer. So I switched to the "PT" type gaskets which are meant to compress and seal without spray on sealers. I am running 10.5 compression with no issues so far.
Hope this helps
