The tensioner rubbing block gets "sliced" up over time running a double-roller chain because the contact area is much smaller; the chain is rubbing on the three small surfaces of the chain links whereas on a stock-type chain the entire width is in contact with the tensioner.
I saw this first-hand on a COMP timing set and tensioner I pulled from my 360 with 25k miles, thin grooves worn into the tensioner pad... this time for my Magnum build I'm using a Cloyes billet true roller and no tensioner.
I have at least 2 spare thrust plates sitting around but if I did need one I'd just get it from the junkyard.
