If that works, use it. You can buy extension springs at the hardware store. You asked about light and heavy and tension. YES it matters but has allowable deviation.
You don't want real small wire size. The length has to work, The spring should not be completely closed, as the artist has shown, when pedal is up. Then it will extend, without over stressing, as pedal is pushed. Look at the pics and get an idea of the proportions compared to linkage and other parts in pic but that is not a photo, so..... anyway....
Oil the pivots. You see they have a swivel tab on one end of spring.
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