Balancer AND balancing questions

I have some seperate but related questions.
Q#1 I am rebuilding and wish to replace my 30 year old balancer with a stock type SFI balancer. I am running an externally balanced assembly with the tomahawk weight in front. The old balancer has no obvious weight built in to assist in the balancing, so is there a difference between an internal and this externally balanced engine's dampener?
Q#2 The flex plate I currently use has the large weight on it. I am anticipating changing to a different trans setup, later in e season, which has (through economic necessity) a neutral balance flex plate. Could I have a heavy metal insert in the rear throw without the exspense of adding it to the front?
Q#3 I am installing a set of Carl's Diamond pistons at about a 320 gram difference in weight from my old TRW's. What are the ramifications of this? Would there be enough difference in reciprocating weight to eliminate the need for the external weights?

The external bal. is in the spacer....the dampners are the same.

You would probably need two slugs of mallory in the rear to "make-up" for the flexplate difference and can't be done without complete disassembly and rebalancing of the rotating assembly which you'll need to do with the lighter pistons.
OR
Have your new flexplate "matched" to the counterbalanced flexplate.

EDIT: With the lighter pistons, you may only need one slug of mallory metal if some metal is first removed from the third counterweight. However, you may be able to internally balance the entire assembly with only one slug in each end.
Whoever does your balancing should know what to do at that time.