No neighbors close by is very nice 8)
Huh, I didn't know Santa Cruz was in the Sierra Nevada's. I thought it was a surfing city on the coast
Plywood with paneling over the top? Could even do a wainscoting over drywall for a "look".
Back in 1980 they were just realizing how building for earthquakes was important, but didn't really start implementing major changes until circa 1985. A box with two door cutouts is about the worst design for earthquakes; think house of cards. I'd recommend just planning to earthquake retrofit it. When you look at the corners of the walls inside the framing you should see metal tie downs and bolts to the foundation often. If not, and I would guess not, spend many hundreds dollars and add some in. Often you will just see nails going down into the concrete through the mud sill. How fast can YOU [scared] exit the building? Easy enough job though. Permitting is required per most counties, but it is an over the counter permit with drawings (Pretty sure on a garage you can use "Standard Plan A" and it could be just hand drawn). Shhhhh, is fine by me as any structural enhancement is beneficial and it is your own house.
A concrete drill can be rented for a short time, but you will need an epoxy gun ($65) or use a strong caulking gun for tube type epoxy to glue threaded rod into the holes. A way to cut the threaded rod like a grinder is necessary. Framing nailer will be needed for putting up the plywood shear walls. A nail every 4" around the outside of the plywood is too many nails to hand hammer, but if you enjoy hand hammering go for it. Minimum 5/8" plywood should be used for shear walls inside the framing, but 3/4" is better for screwing into as you desire. Plywood must be put up by the garage door opening as that is the weakest part of the garage. From there shear walls are needed near or all the way into the corners, on all sides. Sides with doors should be full plywood around the openings.
"Standard Plan A" will explain everything.
http://resilience.abag.ca.gov/wp-content/documents/Plan-Set-A.pdf
Visual of a shear wall, but leave out the blocking at the bottom, as your mud sill should be good enough.
Here is a random article from googling "shear wall".
https://www.finehomebuilding.com/2011/09/08/how-it-works-shear-walls
Each side of a shear wall, gets one of these "Hold downs" below. (DHC Supply has been awesome to work with in person over the years (They do internet sales too), and have great prices.)
https://www.dhcsupplies.com/store/p/5796-S/HDU6-Cold-Formed-Steel-Holdown.html