We'll say it straight: a torsion spring under tension can take a finger or worse if the winding bar slips, and on a door built when yours was, the fasteners and end bearings are often original - meaning corroded, painted over, or just seized from forty years of no maintenance. That combination is exactly when a DIY job goes wrong. An extension spring job on an older door is more forgiving, but you still need to know which kind you have before you touch anything. If your opener still lifts the door partway before straining, that's the spring, not the motor, and it's not a bulb-swap kind of fix. We're not going to tell you it's impossible without the right bars and clamps - plenty of people do it - but we also won't pretend the hardware on a house this age makes it easy.