rage,
Stretching the tubing over the pipes isn't hard, but does require some persistence.
I used 1/2"ID Clearflex 60 thick walled tubing in my system and I manged to get it on the pipes. Boiling water should do the trick, but one pipe is pretty large and I had to use a pair of pliers to "pre-stretch" the tube before wrestling it on the pipe. I heated the Clearflex and stuck the head of the pliers inside the tubing and pulled the handles apart to stretch the tubing. Then I reheated the tubing and it went on much easier.
The pipes on the Chevette HC are pretty tough, you would probably not be able to tighten a steel worm clamp to the point of damaging a pipe. You would risk ruining your tubing though. Tightening the worm clamp too far can cut through the soft tubes, so that should be avoided. When you look at the HC's pipes you will see they have a ridge near the end that will help retain the tubing with just a bit of tightening on your clamps.
Good luck.