The chain or even cable is one way to limit torque over, but what bothers me is that they are solid stops and a violent pull/slam on either when the engine torques over puts a lot of stress on wherever you have it bolted to.
I plan on adding some kind of torque strap on my build, but I want something to absorb some of the initial slam when the slack is snapped tight on the chain/cable. I am probably going to fashion a stop like one of these used on Mopars. Take a look and it will give you a few idea. You might even be able to use one of these if you get your dimensions and email them to see what they may offer. Engine Torque Straps
Another idea tossed around is a solid mount on just the left side and a rubber mount on the right side. It may work, but I am against all the torque focusing on the bolts/side of the block where the motor mount is attached. If I wanted to go solid mounts, I would go with an engine/trans plate as the bolting loads would be better dispersed. They do make these for Pontiac engines, but again, I would not use it for a street car.
You want a little flex so mounts can absorb the torque impact and flex, and absorb vibrations.
Check out the pic of the Fury 440CI police engine torque strap. It is bolted to the engine mount and appears to be on the left side of the engine, so it probably hooks under the engine crossmember. When the engine torques over, the dogleg would simply pull up against the frame to stop engine roll. You can see the rubber bumper pad that hits the crossmember. When I built my brother's 360CI SixPack, the donor engine came out of a 1977 Dodge Charger Dayton. The engine had one of these "snubber" type torque bumpers that bolted to the right side exhaust manifold and sat slightly above the frame rail. This is opposite of the 440CI design, but it does the job in limiting the amount of engine roll by using the right side.