Firstly if you had a GTO you are not a novice, all of the '60s family of GM are similar and share many parts that interchange easily, in fact the bodies are often the same but with slightly different outer panels and trim ...
If you want value for money go straight to Ecklers ( Rick's) Camaro .
They have 2 kits that would suite your needs
1- 67-69 front disc brake Big Brake conversion 13inch cross drilled slotted zinc rotors hubs spindles calipers all for $900
2-C5 Corvette upgrade for 67-69 cars all the features you want -big discs drilled and slotted with special Corvette spindles, calipers and all hardware to mount on a 1st gen .
The stopping power is awesome on C5s and the price is only $650
If you prefer you can deal with a UK middleman who will jack up the price you pay for something like Wilwood, but your car will not stop better because you spent more money ...