Mate, seriously, if you're fitting a 9 second rotary motor I doubt a cage is going to what attracts the wallopers attention!
No offence, but you might want to give this a bit more thought. Hit someone in a car that isn't engineered and you will be paying off the bill for the rest of your life.
Please don't take this the wrong way, just trying to give you another point of view.
Matty