magnum matched to 904

I ran into this issue puttin my Magnum engine in front of a 727.
If you have a trusty trans shop they certainly should be able to tell you.
If they can't they shouldn't be in business.
a good engine builder should also be able to tell you too.

There are 2 kinds of balance weights you might find on a converter.
First they balance all the converters removing imperfections due to manufacturing, there are small thin (postage stamp size) weights on the sides for that. Those are the ones known as "neutral balance" for internal balanced engines,-- or engines that have the balance weights on the flexplate.

Then to correct the engine balance issues they add larger weights to the face of the converter across from the flexplate.
Those weights could be on the flexplate or converter to correct the balance.

what converter are you using?
If stock, what engine was it used behind.