No, everything is different. The Geelong made 250 and Windsor build Ontario 250 are distant cousins, definately not brothers.
In my humble opinion, its a total waste of time doing what you propose untill the aftermarket supplies about 40 different integrational components in one package to make such a set up work. I have been working on a non cross flow head to Cross flow block adaptor since 2004, and an AOD transmission adaptor since 2001. There are off the shelf parts around to make such a marriage work, but no one stop shop. Don't fish for heartache, get a US 250 block
Read Jack Collins Crossflow Chronicles in the Tech section of this site.
The Aussie block is narrower at the motor mounts, about 9.75" wide, not 11" wide like the US one. Oz block is only 9.38" tall, not 9.469" tall at the block to head face. The water pump, ancillary drive, front cover, crank snout, thrust bearing and block bolt pattern are entirely different. Width at the gasket face is like 1.5" wider, and the water conduits are on the opposite side, and the pushrod holes are open in the Aussie block, not closed like the US one
Edge oriface Lifters, oil through pushrods, oiling priorty and the position of the cam shaft differ, timing chain to crank centre is smaller on the Aussie engine compared to the US one. Oil pump, hex drive and distributor differ.
Engine motor mount bolt pattern and some of the ancillary hard dimensions are similar.
