Look under the kitchen sink where the water valves come out of the wall or floor. If they are a rusty brown colored metal they are copper. In 1977 they are probably copper, but California has always had more stringent building codes that most other states. You can also see where the water heater is which type of pipes feed water in and out.
Go under the house or in the basement. You will see the water lines in there. They probably are copper.
Steel pipes are illegal in the UK does that help ?
Yeah it will be fine to run a used axle as long as its not bent.
Both cars use an 8.8 rear axle assembly. Just make sure his axle is the same spline count and length as yours. Some enthusiasts swap back and forth between 28 and 31, or even 33 (drag race) axles. Also, look at where the axle bearing (rear wheel bearing as some people say) rides on the axle shaft and make sure there's no pitting, grooving, or purple-ish discoloration. It must be completely smooth all the way around.
