In my brother's 78 Z28 we used the production 98-02 F-Body clutch slave/throwout bearing. We used the LS7 clutch. This is for a 6.0 L96 and a T56 Magnum. On the clutch master, we bought a Tilton unit from Tick Performance that is sold as an upgrade for 98-02 F-body cars. It's bullet proof but pretty firm. For the 70-81 F-Body, the clutch master hangs on a bracket, that hangs off the studs that secure the brake master cylinder to the brake booster. You just use a stock 70-81 F Body clutch pedal. It's bullet proof.
That solution doesn't work on the G Body. The trick to making the setup work right in a G Body is mounting the clutch master cylinder. Obviously, it can be done since members on here have done it successfully. The firewall itself is not strong enough. It will flex and eventually crack. If I were doing this, I'd use the production 98-02 F Body clutch master and slave/throwout bearing as advised by others for the reliability. You definately want the speed bleeder. I didn't know about them when we put my brother's car together and I wish it had one. Every two years I flush the hydraulic clutch system and having that speed bleeder would be nice.
Some really disparage the factory F-Body 98-02 clutch master as it is all plastic and has a restriction built in to slow disengagement but I would still probably go that way, with a genuine GM piece for the lighter pedal.
I would avoid aftermarket slave/throwout bearings. I've read about too many problems. With the production stuff, as long as the clutch master is securely mounted in the correct orientation, there is no reason not to expect the reliability the production 98-02 F-body cars enjoyed.