Be aware that, on a CZ-455, the lightest spring/shim combinations may result in the bolt pulling (or falling) out of the receiver.
Embarrassing to have bolt fall out in the middle of a stage. Ask me how I know.
A buddy of mine milled a bolt-stop screw into his Manners stock to preclude this issue. He's got that 455 running right - no mods other than YoDave and stock and he usually makes us Vudoo owners look like spendthrifts.
Shipping cost from Canada is absurd - it's import stuff, not YoDave jacking up the price. Hint: you can ship multiple kits for same price as one.