Detination may be as simple as glowing carbon in the chambers or on plugs, but most likley timing issue, all the lifters rattling at higher rpm sounds like oil pressuer probs, did u thiken the oil to stop the rattles? As this might be a prob if you went to thick. The lifters work with oil pressure if the oil is to thin or too thick it afects the lifters. I would time the motor first then take the rocker cover of and start the motor to see if you can nip the rockers which may be loose too . Good luck