My car was 1850 with 5 gallons of fuel in the cell and had an easy 100 pounds that I could have removed. I had to run that much fuel as the cell wasn't installed properly and it would have fuel starvation. I dropped a bunch of weight from the front hubs/brakes when I redid them to lose much lighter Wilwood calipers. Someone had spent hours grinding the 4-piston Toyotas down to the size of a Wilwood Dynalites. Hubs were steel and couldn't have been changed to Aluminum. Car had a steel driveshaft, R200 diff, and all the stock crossmembers. I had a super-heavy Optima deep cell battery (65 pounds) because I had alternator problems until I switched to a modern Kubota tractor version. All in all I thought there was an easy 100 pounds of weight I could have removed getting the car into the 1750 range. I've seen other Z's that low so mine isn't an outlier, just not a normal compared to most.
Wheels, tires, brakes, clutch/flywheels, transmissions, subframe braces, all are hidden weight that really adds up. Even too much MIG welding. I started to look more and more at modern panel bond techniques as a way to save weight. Riveting brackets that didn't need to be unbolted, etc.