You can purchase a crossflow head in Australia for $100, but it will cost $200+ to get it to the US. You will then need an intake and exhaust manifold specific to the crossflow; and don't forget the crossflow cam.The problem with the crossflow block is it has a different bell housing and all, right? I've seen the article for installing it on a precrossflow block, its fairly intimidating but I have a spare block I can practice on. if the head is only like $100, I'd be interested if you'r willing to help get it shipped here to Seattle
If you had a crossflow block, the main bearings are specific to it. The rod bearings, pistons, and other parts from the US 250 can be used. The crossflow bellhousing bolt pattern is specific, but a 4 speed BH can be found and a T-5 adapter plate used.