[Mgs] MG flywheel. Is there balance in our MG flywheels?

[cyberemp at comcast.net]

your note turns up a question that has engaged me for some time. 
Is there balance in our MG flywheels? Years ago I had the engine to my MGA balanced, with the flywheel turned and a different ring gear installed. 
There were no marks or instructions on the orientation of the flywheel for installation. 
Recently I had the balance of the flywheel of a later (76-80) MG checked, and was told that it was not a perfect, or neutral balance. 
I could find no markings on this flywheel for instalation either. 
Is it possible that this variance is due to the motor involved? 3 main bearing verses 5 main bearing? 
When rebuilding the engine of my first car, a 1967 Ford Cortina GT, I was told by my my mentor to make small marks on the flywheel and on the crankshaft end so that I could reinstall the flywheel in the same orientation, in the hope that the original assemblers in the factory had known what they were doing. He said this with a smile, indicating a bit of doubt as to the attention given to this matter. 
So I offer this question to you, my fellow enthusiasts. Is there balance in our flywheels? 
Eric. 
46 MG-TC 
59 MGA 
65 MGB 
70 MGB 
71 MGB 
So many cars, so little parking.