Springs and cables under tension are not a weekend project, full stop, and that's true everywhere. What's specific to a place like this is the hardware age: a door original to a 1970-built house is old enough that its torsion spring, if it's even still torsion and not an older extension setup, is sized to a door and drum combination that current stock doors don't match. Swap in a modern door on old track and you've got a mismatch that shows up as noise, drift, or a door that won't seat square.
We'll say plainly what we won't do: we don't sell a door without checking the track and header first, because a beautiful new panel on a bent rail just fails again in six months. If you want to handle the trim work or the opener wiring yourself, that's fine - leave the spring, the cable, and the drum work to us.