My 2c..

Bolt in rear coil overs for a 1200 do not exist.

The mounting points for the rear shocks are not designed to take the loads that coilovers will place on them, especially if you use them for height control.
All 3 1200 rally cars I have had has had some sort of seperation/damage to the top rear shock mounting points even when used as normal shock mounts (admittedly a much harder life than a street car), start putting sprung suspension loads through them and it is a recipe for disaster without substantial strengthening..