I did this to the old LX sedan and hatch a while back. The sedan was Torana pattern and the hatch HQ.
I think there was a theory that the wagon handbrake cable was longer than the sedan one?
While I didn’t have a problem with axle slop that might have been dumb luck. Both conversions were on nine inch diffs which probably had disc brake seals fitted when they were built.
“Perhaps not bolt on but certainly not hard.
Did this recently to the LX sedan.
Went to wreckers and bought complete rear brakes off a VS wagon ie backing plates, calipers, discs, handbrake cable and rear brake lines.
Had torana pattern drilled onto discs (apparently this is fine and was done by romack UPC in melbourne).
Pulled old brakes off.
Bolted commodore backing plate to diff flange (same bolt pattern)
Add disc.
Bolt up calipers.
Add brake lines with ends changed to suit ($5 by the local brake place as couldnt find my flaring tool). Had to use the long orig torana line and one of the commodore ones to get lengths right.
Bleed brakes.
Add handbrake cable. Find out it is tantalisingly close but slightly too short to meet torana threaded rod.
Weld 4inch long piece of flat steel to commodore handbrake cable front grabber and bend end of flat at 90%. Drill hole. Add nuts x2 and adjust.
Total cost:
Wrecker bits $140
Redrill discs $40 for both
Redo lines $5
Make longer front handbrake "pickup" - zero (scrap from shed pile)
Brake fluid $5
= $190
Total time including retrieving bits from pick a part - about three hours.
The braking is much improved over the well adjusted torana drums.
Has the unexpected bonus of giving a somewhat firmer more confidence inspiring pedal feel.
If I had realised how painless it was I would have done it years ago.”