The only truly legal way would be to take it straight out of a cobra r along with every single piece of emissions and exhaust equipment, then take it to the state referee and get an exemption sticker.
If you get it dirty enough and make it look like a 5.0 they won't know the difference. Not sure if there would be ecu issues when they plug in, im not very familiar with the pushrods. I have a clean engine bay and they ran all of my serial numbers when I went to get smogged. Once they failed to find anything wrong with my serial numbers they failed me on "visual smoke" which was just BS because they didnt want to pass me.
Why not just put a stock motor in to get it smogged and then swap it out?