to break 1000 is tough but possible. (is only really acceptable on a track car)

you need to get rid of as much steel parts as pos and install Carbon/Kevlar,
Doors, rear hatch, bonnet, bumpers, sills etc.

Remove complete braking system and install pedal box and remote cylinders.

Remove power steering pump - install electric or Hydraulic/electric. (if Hydaulic/electric, install motor/pump under front wing. for electric, install motor on steering column).
5kg can be saved if the complete column is reworked.

Track car only. (due to cost and extra work).
the original Ford loom is very heavy, lose as much as possible or renew the complete loom and fuse box. lighter battery in the back.

Remove complete fuel system and fit smaller tank and pump and lightweight hose with alloy connectors.
remove all original seat fixtures, use lightweight tubing as fixing rails.
all brake calipers exchanged for lightweight alloy items.
all plastic windows except front.
remove complete heating system.
alloy tca's
GpA engine mounts, modify front xmember.
get new steering rack from Titan Motorsport. (to be used with electric motor).
how far do you want to go?

start with the cheaper options and weigh parts as you take them off.

please let me know if you find a way to reach,
600kg front
400kg rear

have fun

kenny.
ps, 400kg rear is quite easy.