[SFfiredog]

You will need to determine the true deck height of the block.
The stock deck height of a 427 is 10.17"
If the crank, rods and pistons are correct then that means your block has been cut .040" to .050".
If you care to use a block cut that much custom pistons will be required.
You will alsohave tons of fun getting the intake manifold to fit and of course custom pushrods will be required.
I hope your block is not cut that much and you will just need new (correct) pistons
--Mike