For a house built around the 1970 mark, the cable gauge and drum pattern tend to run consistent with that era's standard torsion setups - that's most of what we stock on the truck for calls out this way. If your door's had a partial upgrade at some point - new opener, newer spring, but original cable and drum - we bring parts sized for both the old and the newer hardware, since mixed setups aren't rare in a town where houses are closer to 55 years old than to new construction.
What we don't carry is anything obscure or discontinued - if a drum or cable spec turns out to be a one-off from a builder nobody else used, that's a special-order part, and we'll tell you that up front rather than pretend otherwise. That's the one honest limit here: most cable jobs on 1970s-era doors are a same-truck fix, but the occasional oddball build means a return trip.