so, let me start and ask what cars can donate brakes
Front brake upgrades usually consist of swapping the entire strut. As such:
Mild front brake upgrade = 80-83 200SX (10" solid rotors, stock 510 is 9" solid) These will allow you to run the 240Z 2-piston caliper or Toyota 4Runner 4-piston caliper, though
Better upgrade = 79-83 280ZX (10" vented rotors)
Crazier upgrade = 84-85 300ZX (11" vented rotors)
And brackets are available to use the 300ZX 11" rotor, on the 280ZX strut, with a Wilwood 4-piston caliper. Big $$$ but sexy.
Rear brake upgrades usually consist of custom brackets (available from a few different sources) and then using rotors/calipers from the 79-83 280ZX, 80-83 200SX, and 80-84 Maxima sedan
Shocks is the usual. Up front you need inserts for a 79-83 280ZX, either in standard KYBs, adjustable KYB AGX's, Tokico Blues, adjustable Tokico Illuminas, or whatever your wallet can handle. Same for the rear except you need shocks to suit either an 84-87 RWD Corolla or 82-91 Camaro.
These applications gets you shocks that are 1-3" shorter than stock, ideal if you're planning to lower it.
and suspension like A-arms, subframes.
As he said, there's really no such thing on a 510. The stock lower control arms and crossmember works just fine. Unless it's missing, there are no "upgrades" to be had.
There are modified lower control arms out there, if you need more adjustability or want to do away with the rubber bushings and go to bearings.