will any automatic counterweights work if I'm using a steel/lightweight flywheel?
I want to get an 83 front counterweight from a junkyard, but if I can't use it with my 84, then I won't bother...

 

Your post a little jumbled.

Are you trying to install a lightweight flywheel? If so you need the rear automatic counter weight off the year of your motor, but they are grouped like this.

12A
- 79 thru 80
- 81 thru 82
- 83 thru 85

13B need a Rx-4 unit.

You do not need the front counter weight if you are only putting on a lighten flywheel.

If a different front counter weight is installed, then you are going to have to have the engine balanced.

John

 

Well, I know there are different types of lightweight flywheels. What I mean to say is that if I wanted to put on a lightweight (not a stock lightened one) flywheel, say, steel or aluminum, and I have a '84 12a, could I use a front counterweight from an 83 automatic?
Going by your chart, it seems that I can, but I thought the rotor weights were different from 83 to 84, thus differing counterweights.

 

You need to understand what you are asking, if you are going to install a lighten flywheel on your '83 motor you will need the REAR counter weight from '83-85 12A engine automatic car.

You keep saying front counter weight, which you do not need if just installing a lighten flywheel either aluminum or light steel.

All rotary engines have front counter weights, on the automatic cars added a rear counter weight because the flex plate could not balance out the motor with out it.

MazdaTrix confirms the rotor weights.
rotor weight chart from mazdatrix