Cages can be pretty heavy, depending on what they are made from, and how comprehensive they are.
I had my ae71 with 20v conversion, ae86 diff, bigger brakes. Tools in the back, full interior minus carpet and door trims, spare tyre, all seats etc.
It was 1060 with me in it. That was on the weigh bridge at the dump.
If you deduct all the loose crap and myself you are looking about 930kg, near enough to what the book says.
Vehicle weights are the most lied about shit amongst car enthusiasts.
I had a guy tell me once his ke70/7age was "about 700kg". Thats with a celica diff in it too.
He had a full interior minus sound deadening, no other weight reduction to speak of. I said ok then you should spank me in a race, 1.8 litre/700 kg vs 1.6 litre and 1060 kg. So we lined em up and he got pantsed.
Do not believe everything people tell you.