If you convert to disc, you will need to change out to a LT1 prop/ABS unit since drums don't require as much pressure as disc do to operate properly, spo the calipers may not function correctly. Also, drums need residual pressure to prevent the pistons in the wheels cylinders to retract fully. This may prevent the pistons in the calipers to retract fully, making them push up against the rotors.
3.23's are the only rears the 3.4 F-bodies came with ( Manual & Auto) in 96+ the ratios were either 3.08 (Auto), 3.23 (Manual) or 3.42 posi ( Y87 performance package)
If you are to go rear disc, may I recommend LS1 setup. I find it more reliable, and with the hat system, replacing pads is a sinch. You will need to change your front parking brake cable to a 96+ because it is slightly longer to accept the LS1 cable lines.
Oh, and I have both LS1 and LT1 full sets for sale if interested
