I put the Right stuff kit AFXRD78Z from summit racing back in 2020 They were a lot cheaper than today.
Installed new axles and bearings at the same time and new proportioning valve for Disc rear brakes.
Zero issues with this setup.
pictures are on the 2020 thread Rear Disc Brakes.
BRF 1986-1987 Grand National, Turbo T, T-type
BQ 1984-1985 Grand National, T-type
BR 1983 T-type
TAF 1989 Turbo Trans Am
CZF 1985-1988 Chevrolet Monte Carlo SS
CRF 1985-1988 Monte Carlo 305 engine LG4
KZF Oldsmobile 442/Hurst
OZ 1983-1984 Hurst Olds
OM...
Finding 84 GN interior parts will be very difficult to find even harder in good condition.
I know from years owning one.
Most items are discontinued sometimes seats show up but in poor condition.
Sand fabric is out of stock
Checkout Gbody Parts they may have sand paint and some parts
Good luck...