Just my opinion, and I'll readily admit that I'm biased

, but the primary reason to run C4 front brakes is because you can't fit C5 or C6 brakes. If you can fit C5/C6 brakes, there are a lot of benefits to doing so including stiffer calipers, bigger pads, pin-guided design (versus pad-guided), and thicker 32mm rotors (versus 28mm). If a standard C5/C6 kit won't fit inside your wheels of choice, then you might consider giving Noel at Touring Classics a call as he sells a C5 kit for the 1st gens that uses the deeper offset (but also narrower) C4 HD 13" rotor. I would go that route long before the C4 kit.
The POL kit that you linked to shows spindles...do you need spindles? It also shows hubs...do you need hubs? All things to consider if you're trying to do big-brakes on a budget since odds are that the spindles you have are serviceable, as could be the hubs with a little work if you've got a drum/drum car. If you have a disc/drum car, then you will need hubs, but there are better alternatives than the cast iron OE replacements I've seen around (some of the imports are highly questionable with respect to quality).
As for the master cylinder that you linked to, the 1" bore is going to be marginal with the C4 front calipers (bore is too large), and admittedly, I'm not a very big fan of fixed "GM spec" proportioning valves. It doesn't make sense to put a stock type proportioning valve on a vehicle with nothing stock on it. You're lowering the car's center of gravity, adding performance suspension upgrades, different (hopefully better) tires, etc...an adjustable rear proportioning valve should allow you to tune the rear brakes so that you're getting optimal performance from them.
Tobin
KORE3