I have two thoughts, The coated brearings DO ADD to the overall measurement even tho they say they dont in some of there literature. Clevite bearings have worked for years, there still good now too. Another thing is on the Dart blocks you must hone the lifter bores to get the proper clearance. If you dont then when the heat comes they will seize the lifters in the bore and hold the valve open and then kill it. I would think that it wouldnt be your problem with several passes already on your motor.