Fairly sure the port spacing on them is the same - but due to the mk2 have a remote oil filter thing, and the mk1 having it directly on the block - the pipes on the manifolds are routed differently.
I'm sure some of the aftermarket manifolds are made to suit both mk1 and mk2 - i know the BTB i have for sale is advertised by GMC as for Mk2 but fitted my Mk1 fine as well.