Best bet is to go with a HydroBoost from an aftermarket supplier.
Spend the money one a current unit that is gauranteed to work . Don't gamble on a re-man 84-85 unit (which have a high failure rate).
The newer units feature an accumulator & are best as they give an additional 2-3 stabs at the brakes if you loose your PS pump.
HydraTech, Talon Hydraulics (now Vintage Speed Reaper), CPB, etc. are just a few names for you.
Most of these are current Bosch HydroBoost units (who own the HydroBoost trademark name) , unlike the 40+ year old technology used on the 84-85 Buick HydroBoost systems.
Only downside is the price...you should expect to pay just under $1K, but includes SS braided lines and AN fittings.