New cam...loud clacking lifters. ???

Hi, Hope someone can help. Installed XE268 cam and lifters in a stock 318 with carb/intake. Fired it up for break in and very loud lifter noise...thought they would pump up ran thru break-in. Noise never went away, had small oil leak at back of intake, took intake off found 4 bent push rods and lifters completely pumped up. I ordered OEM pushrods and put it back together, noise still there, very loud clacking lifters. Called Comp Cams, they said to check pre-load, did that, found "0" pre load, OEM pushrods undamaged, ordered .050" longer push rods, took a vacation day today to install them....noise still there...sounds like a diesel idleing!