A friend of mine has a 70 Impala cab. with ZZ502 engine. The engine rocks from side to side at idle, it seams that like the engine mounts are diffrent from left to right side, the left appears to be softer than the right.

Are they suppose to be diffrent ?

the motor mounts are the same, left and right. does he have a broken mount?

I'm not sure that one is broken, but the left and right are not the same type.
I think we will get a new pair of engine mounts.
Could anyone post a pic. of how they should look?

For 1969-'72 the motor mounts were interlocking and bolted the vibration isolator to the motor. Your rocking has a lot to do with the low to midrange torque produced by the ZZ502. That motor is putting out over 300 lbs ft of torque by 2,400 RPM (just off idle) which is what a stock 350 makes wide open.

It is a powerfull motor :) thats for sure, but a 900 RPM it feells like the engine is popping out. It should be more steady.
Anyway, a new set of engine mount is in order and will be changed, I will let you know of the result.