Turna, Thanks for the heads up on this master.
These later model S-10 master cylinder are great, but there are some things to keep in mind.
The outlets on this s-10 master cylinder are both 1/2-20 inverted flare. (Correct me if I am wrong).
The rear outlet of most g-bodies for the front brakes is 1/2-20, which will bolt up to this new S-10 master cylinder.
The front outlet of most g-bodies for the rear brakes is 9/16-18, which will require a new brake line with the correct fittings or an adapter fitting.
The adapter fitting to mate the stock brake line to this S-10 master cylinder should be either Edelmann PN 258306 or 258307 (I can never tell from the description which is which). This will be the easiest option.
The other thing to keep in mind is that from 1982-1988, the front g-body calipers came from the factory with LOW drag calipers. LOW drag calipers require a step bore master cylinder because the front caliper pistons retract away from the rotor more than a normal caliper. A step bore master cylinder uses a 1.25" volume bore to move more fluid and push the caliper piston back up against the rotor. Once the pads are back up against the rotor and the pressure in the system builds to 100 lbft, then the master cylinder transitions to a smaller 24mm bore for more pressure and substantially greater clamping force.
This S10 master cylinder has a 1.0" strait bore master cylinder. If you still have your stock, original, from the factory calipers, you will need to replace them or you will have a pedal with a longer pedal travel. You will have a longer pedal travel because the 1.0" strait bore master cylinder will have to move more fluid volume to move the LOW drag caliper piston back up against the rotor before it will start to build pressure and caliper clamping force. Any stock replacement, new or remanufactured, caliper should be a NON low drag, normal calipers. All caliper part numbers are the same for 1978-1988 g-bodies. 1978-1981 calipers, from the factory, where NON low drag, normal calipers and they used a strait 24mm bore master cylinder. 1982-1988 g-bodies calipers, from the factory, were LOW drag and used a step bore master cylinder. A strait bore master cylinder cannot be (or should not be) used with LOW drag calipers, but a step bore can be used with NON low drag, normal calipers and LOW drag calipers.
Just keep these things in mind if using this as a replacement master cylinder which is a great alternative.