I dare say the easy way around rego would be to copy the number from your old block to the new. If you wanted everything by the book you would need (in NSW in any case) to stamp a new number on the new block and attend an appropriately licensed workshop to have a blue slip and change of engine number documentation completed. I had to do this years back when I swapped engines on my 260z. Being in excess of 20% displacement and not being an engine from the original manufacturer you would also need an engineer to sign off on it (item 1 http://www.rms.nsw.gov.au/documents...ndards/vsi-06-light-vehicle-modifications.pdf) I dare say those looking to actually commit to something like this wouldn’t be too fussed on doing things by the book... I mean if we take that approach the moment you increase power above 246rwkw, fot larger valves, fit an aftermarket exhaust, remove the EGR, fit an aftermarket air filter, upgrade injectors, etc etc you SHOULD be lining up to have the modifications engineered.
Or for the dodgier among us, stamp the new ally block with your existing block number and keep the iron one in the shed or destroy it and bin it.
Well i beg to differ. I think the definition of fitting requires it to be inside the car. I have a 300 with a single throttle body that does not fit in my 300zx. Now i like the single throttle body a great deal but because it "Does not fit" i hate my bonnet bulge, it looks like someone couldn't measure. I'm not taking anything away from the guy that put the gtr motor in his 300 he is, from memory, interested in drag racing and drag cars look ugly so it doesn't matter.
THIS, in fact I would go and buy and old engine that has a buggered block and use the number off that..... When you get a block skimmed about half the time the number gets machined off anyway and has to be re-stamped. The engine number would have VG****** anyway and I expect that it would sail through an RTA inspection with no issues. You can increase stroke and bore diameter with sleeves in a stock block and have no issues with compliance. This is no different...