I need an eduction in Cog Setup

I am running a YS Trim on my small block 427w with a cog setup. Can someone give me the basics of setting up the cog pullies? I have the thicker than stock mounting bracket and the turnbuckle that goes to the strut tower and we can't keep the bracket from flexing. Everytime we go over 5000rpm on the dyno it throws the belt. I am sure it is an alignment issue, but I don't know what is the correct way to set it up. Thanks

Perhaps its not tight enough, or too tight ??

Only way to align, is to make sure both pulleys are 100% true to each other, when belt is tight...although not sure the best way to check that

Does your idler have a lip on it?

Yes, the idler has a lip on it and so does the crank pulley. The blower pulley does not have a lip. Thanks.