Hello.
I'll try to give you a few pointers.
In addition to internally and externally balanced engines, you MIGHT come across a "thrown together mix of the two".
Some unfortunate buyers, have a combination thrown together by ignorant wannabe machanics.
Mechanics who believe that as long as the parts physically fits they'll work in harmony.
Persistant vibration problems will be the result.
With that in mind, my advise is to find out of your
engine/trannsmission combination appears to be working OK as far as vibrations is concerned... Call the privious owner if in doubt...??
IF VIBRATION LEVEL even at hight speeds and revs are acceptable, my advise is to replace EACH of your old part with a similar new one if needed.
Example. Even if your engine originally had a cast crank, and was of externally balanced design (with matching harminic balancer in front, and matching externally balanced converter) there is still a possibility that this crank has been put in a machine and INTERNALLY BALANCED (together with your pistins, rods, etc...)during a proper overhaul. During this overhaul, each part has been balanced, or replaced by a balanced part.
This is what I have in one of my cars...
That was the the differcult answer.
The simple answer is, take a picture of the harmonic balancer (front crank pulley)
We should be able to tell you is this balancer originallay was of type internal or external balanced type.
Same goes for the converter for automatic, and I assume also for the clutch.
Provide pictures, and I'm sure someone can find a book and tell you what you have.(Of external parts at least)
AGAIN, IF your combo is causing heavy vibration, the culpit MIGHT be a mismatch in your engine/tranny combo, and you really do not want to just replase incorrect parts....
SORRY if my answer caused more confusion than clearification....