BKO = Bronco. If the seal is not leaking, there is really no need to replace it. In the pic above, the blue part of the seal doesn't do anything. The part that actually seals is the dark brown part that goes right up against the crank shaft snout.
Does your motor shake while the car is stopped, while the car is moving, or both?
If the motor is shaking, start by checking the motor mounts and tranny mount first. If they look to be in good shape (no cracking or tears in the rubber), then remove the pulley and balancer (AKA dampner) and visually inspect those. Make sure the pulley is still round. I've never had any problems with a balancer, but IIRC, there is rubber in the ford balancers that attached the hub to the outer portion. That rubber can wear out, tear or crack over time.
I haven't had to get that far back into my motor yet, but on the 5.0 you basically have to remove all the accessories to get the timing cover off. You're doing as much work as replacing a cam shaft without actually replacing the cam shaft.