A new install looks like a weekend project until you're standing under a 150-plus pound door section with no third hand. The part that catches people in homes from this era specifically is the track alignment - framing from 1964 rarely reads as perfectly square on a level today, and a door that looks fine standing still will bind or jump the track under power once it's moving. Winding a new torsion spring to the right tension is also not a place to guess; the springs sized for older, lighter doors are wrong for a new insulated door, and an under- or over-wound spring either won't lift the door or will slam it down hard enough to hurt someone. If you're comfortable with framing carpentry and have someone to help hold panels, you can handle the parts that don't involve spring tension - trim, weatherstripping, final hardware. The lift mechanism and the spring are where we'd tell you to stop and call someone, in North Haven or anywhere else.