When replacing any high-tension spring, the obvious problem is that you have to over-power the spring to install it. The stronger the spring, the larger the problem.
Here's one method that might help.
For our example we will use a clutch pedal spring on a 1967 Barracuda, with 383 cu. in. engine, 4-speed transmission, and console shift. In this instance, when the clutch pedal is removed (for any reason) the clutch overcenter spring must also be taken off. It is difficult to reinstall this spring, partly because of its heavy coils and partly because there is a limited amount of working space.
One way to make the installation a bit easier is first to secure one end of the spring in a vise. Then use a suitable bar to curve the spring in a manner that opens those parts of the coils that face downward when the spring is installed in the car. Place six to eight large flat washers, about 3/32 in. in thickness, between the coils and release the bar. This keeps the spring extended so that it can easily be installed.
With one end of the clutch spring in a vise, use a bar to open the coils to insert flat washers.
When the spring is in place, use a large screwdriver to pry open the coils. This will allow the flat washers to drop to the floor, and the spring to exert its normal force.
This same method can be applied to other applications as well.