I've dropped many engines in with the harness. I feel more comfortable using the harness than the "plate" that bolts to the carb flange on the intake... I don't want the engine and trans to be supported by 4 x 5/16" bolts vs 10 x 1/2" head bolts on each side... I usually have the intake bolted on, but he had his LD340 powder coated and I don't want to mark up the finish with the brackets from the harness...
We chased all the threads for the heads and bolts, so we should have good clamp load and it shouldn't affect the head gaskets... (I hope...)
I always chase my threads with a tap and die to make sure that they are clean and good, that way you get the proper clamp load when you torque them... Very important... Plus the parts go together much better when you do...