If so.....to use unicast rotors.....can I just use F/J/M or A Spindles?
Without getting into the whole FJM spindle debate, yes, they will bolt on. This would also includes any post 73 B body and R bodies as well.
The debate about the viability of these spindles is long and ugly. Suffice it to say that the two mopar mags and their respective tech editors, are on opposite sides of the fence about it.
So you are going into it with your eyes open, the taller FJM spindles are 3 pounds lighter and 3/8" taller. This additional spindle height raises the roll center location 1-2" over the A, pre 73 B, and E body spindle. If you have turned down your torsion bars to lower your car, this change can provide a benefit to the handling of your car. This additional height also changes the location of the upper ball joint. This new location allows the suspension to gain an additional couple of degrees of camber as the suspension compresses. This is a benefit as it keeps the tire in better contact with the road during cornering. The price of these gains is some additional bump steer. At 4" of compression, this adds up to additional .06 inch worth of bump steer. However, even this is not all bad as the bump steer creates slightly more toe out during the turn which can add more ackerman effect which will translate to a better feel of stability to the driver.