Balancing pulleys 264ci. 55' Buick Special

[btate]

Let say I for some reason I replaced my single groove pulley with another single groove from another car. Would I have to have the whole engine re balanced? Since the pulley is balanced with the flex plate. My true goal is to replace with 264 ci 2 groove pulleys

[JohnD1956]

The answer is probably yes, but I don't know that for sure. What I do know id the Service Manual procedure to balance an engine seems to be a hit and miss type of thing. Clay putty inside the balancer hub, guess at weights on the torque converter, drilling excess material from the torque converter, etc. So the practicality is, change the pulley and see if it makes a perceptible difference.