I have a set of Isky 3970-HYRT lifters. I was going to run them in a mark IV. I now have a dart based 540. I was told by Isky that they will work in a Dart block. I didn't think they would work in Darts tall body lifter block. They are reboxed Merrels I guess. Also, how much lift cam I run for a 6500 rpm motor. I am running a set of Jessel pro 1.8s on a set of AFR 357s. Thanks in advance!