texas has emission testing, and with an engine, that is typically your "legal issue".

no engine is just plain illegal, due to size or power output, but in many states engines are illegal because they dont come in a stock vehicle. for instance, in PA and i think CA, if you change the engine, you have to put in the same engine that you took out. the mirada has a 340 in it, so it can not even be checked for emissions. this is much more true for any OBDII vehicles (95 and newer), as the computer wouldnt know what to do with the bigger engine when swapped.

however, in michigan, ohio, west virginia, and im sure there are more, i could put that 540 in any of my vehicles, and drive it around.