Here is another important safety improvement for your Amphicar.
If your Amphicar has it's original (or older replacement) rubber brake lines, you should do yourself a favor and replace them ASAP. Why? After years of use, they will get clogged up and begin to act as a one way valve. The fluid will be pushed into the wheel cylinders, but the cylinder springs are not strong enough to push the fluid back through the clogged lines. This will cause your brakes to not fully release. Then the brakes heat up, eventually boiling the fluid, creating even more pressure on the brakes. You will soon be unable to move the car at all. This can even cause the brakes to catch fire. Sometimes the only way to move the car is to cut the line to release the pressure.
This is a cross section of an original brake line. Notice how the line is virtually closed. It allowed brake fluid to flow freely to the wheel cylinder, but would not allow it to return.
The yellow circle indicates how large the opening would be in a new hose.