Slant-Six to LA small block conversion.

Agree with the above, as far as similarities to U.S. go; the transmission and radiator will be the issues- your driveshaft should work. But, since the Aussie Val is RHD, I'll leave speculation on the minutia to our members down under. Things like the throttle linkage, steering box and column clearance for the RH (driver's side for you) exhaust manifold, and engine mounts on the (slightly) different K frame, and how your RH steering column shift linkage connects to the left side control levers of a 904 may be issues. I do know that the 273 required use of a remote oil filter to gain steering column/box clearance, and since all LAs are similar, they would likely all need the same. But since these were factory offered, they should be easily dealt with by comparing to a factory 273 Val and using factory-type parts.