I was wondering for years why GM put a hard line instead of a brake hose on the rear left caliper on the 82-88 delco morraine system. Does anyone know what sense this makes? I mean, they put a hose on the passenger side, why not on the drivers side? I almost had a heart attack a few days ago when I did a brake job and the caliper fell of the construction I made to hold it a bit away and almost hit the ground and bent this stupid hard line.
Anyone ever figured a direct fit replacement hose for the left side that can be installed? I have a flaring tool and everything it needs to shorten the hard line and install a hose there, just looking for samples. IMHO this is one of the dumbest construction on these cars... On the left side you have the hard line that can't be moved or bend to hold the caliper away and on the right side you have to remove the trailing arm to get access to the caliper bolts.

 

Historical research on GM and disc brakes isn't likely to lead to any answers specific to your particular question, so unless somebody on TGO was part of the process back in the late 60s/early 70s when this was probably designed, then all you're likely to get is speculation.

Regarding what you want to do, it'll be simple to replace that driver's side hardline on the axle with an 89+ hardline. You'll probably have to purchase the pair of hardlines, left and right, but they're cheap.

I don't know if there are any sources overseas, but here are two in the US:
Rear Axle Brake Lines | SSTubes – Tagged "Chevrolet-Camaro-1989"
Inline Tube | Preformed Lines, Brake Products, DIY & Restoration Parts