No the US head will not work on the crossflow block. The crossflow block is wider at the deck surface than the US block; that's why a 1/4" plate has to be installed on the US block to use a crossflow head on it. You'd be better off buying the crossflow block, then finding a crossflow head to install on it. Several people on this forum have extra heads they may part with, or you can get one off Australia eBay and have it shipped. The alloy crossflow head is light enough to ship.
Do you know the casting code on the crossflow block? Early crossflow blocks used a rope seal similar to the US block. In 84 they went with a one piece seal, then in 86 went with a larger seal used in the SOHC engines since they were built in the same factory.
The crossflow engine is narrower at the engine mounts than the US 250 engine, almost the same width as the US 200. This allows the engine to sit lower than the US 250. The crossflow oil pan is narrower than the US 250, almost a hybrid between our 200 and 250.
Hope this helps.