As R33-Racer said u would have to have really low comp to make it "free running"
You would need serious bowl pistons or a lower top dead centre.
To give you an idea, a stock RB30ET is in the 7s and is still an interference motor.
To test it: remove your timing belt and crank the motor over by hand if it hits a valve you know the answer. keep trying this with turning the cams a few degrees and cranking it by hand, ull get the idea.
Out of all the interference motors with broken belts that have come in through work only 1% have escaped the carnage. There is a very small chance that when the timing belt snaps that the cam/s will be in the right position so all the valves will be shut/ clear the pistons.