Didn't read everything but heres a few things.
Can't for get the tires, buzzing/humming sound could also be cumming from the tires. May need balancing or may need to be replaced because of flatspot (cupping).
Bumpers, the pre '88 cars came with metal bumpers which stick out about 3-5" from the body, if they're not out that far then may have drilled rebars or been in accciedent.
Suspension, drive the car to about 70-80mph (thats about 120kph) if the car starts to bounce or sway may need new suspension. Some degree of bounce is normal for the wieght of these cars.
Springs, people often lower these cars by cutting the springs, or compressing them with clamps, resulting in some degree of bad handling.
Cluster, if two or more gauges in the cluster do not work may need a new board thats $200-500 USD.