I used the 440 source flywheel on a 70 Cuda 440 6 Pak. I found that this flywheel appeared to be the same as one sold by McCleod. The difference is, that McCleod sells different weights for the different engines, and they also have a diagram in their site, that shows which pair of holes to put the weight in. So I bought the proper weight from Mccleod, and all is right with the world now ! Or, at least this six Pak doesn't shake !