I have a 88 rollerblock and am going to replace the timing cover with one for a mechanical fuel pump.The timing chains in Summit ask if i need a set with 1 or 2 piece eccentric.This is going in my 68.
I know the later models used the two piece eccentric, and I can tell you that a one piece eccentric will not work if you want to use a early model timing cover on an early block.
the two piece is thinner than the one piece. I had to use the two piece on my XB3M 345HP Ford crate motor , with an early front cover. The one piece would not clear the front cover. timing chains are different as well. the double roller chains can hit the block around the crank gear. look very closely. i have three new chains hanging on the wall. manufacturer's make a slightly different chain and the machining of the block definitely affects which chain you can use.