The rods in those older motors have a tencency to kreep and bind when rolled by hand. This does not happen when running because they will self center but is un-nerving when setting up.
I have found that aftermarket large end roller are not good. When setting up my 6 I had purchased some aftermarket rollers from the S company and found that it appeared I was missing a roller. Could not put in another roller. Got checking the size of the aftermarket roller and found them to be 2-10 thousands under size. given the number of rollers, this amounts a considerable gap increase and that is where the crank journal under load wants to go.
As for using later model rods, they changed the wrist pin size in the mid to late 60's and the piston does not have enough stock.

Also attached a new previously unreleased Beast photo.


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