What year 351 do you have? Some take a 2pc eccentric with the Edelbrock chain set. Go to the Edelbrock site and click on valve train parts, then timing chains, it will tell you part no's and applications for using the two pc one. If I remember right the one piece is wider. The two pc one's I have measure .830 wide, can't find a one pc so I can measure it. Also most after market cams come with two different length dowels. Made a mistake one time installing a long dowel in one and it was'nt quite flush with the cam and the eccentric would not bolt up square, thank God for electric fuel pumps anyway. Hope this sheds some light on the problem.