Ford changed the balance weights more often than a woman changes her mind. I always get the flywheel/ring gear with the engine if at all possible, but in your case that wasn't feasible. Get hold of a GOOD Ford parts man, and have all your engine numbers with you, and you might get a combo that won't shake itself to death. I've had 302's and 351W's that shook the screws out of the dash in seconds.