For a town built mostly around a single decade, the parts we carry out don't vary much - torsion springs sized for the standard door weights common to 1960s single and double garages, extension spring pairs with current safety cables, and winding bars sized to the shaft diameters that turn up on this era of hardware. We also carry the drums and cable that often need replacing alongside a torsion spring, since the two wear together.
What we don't stock on the truck is anything custom - a spring for a door that's been modified with an odd panel weight or a non-standard track conversion sometimes means a return trip once we've measured on site. That's rare, but it happens on houses this age more than newer ones, since a lot of these doors have had at least one panel swap or opener retrofit over sixty years that changed the load without anyone recalculating the spring.