Thought I might add this information for those who have hydroelastic suspension , this is the recommended measurements and pressure for the system .

Early cars (up to late 1965)

Ride height (from wheel centre to top of arch): Front: 324-336mm Rear: 337-340mm
Pressure: 263psi
Later cars (late 1965-on)

Ride height (from wheel centre to top of arch): Front: 315mm-350mm Rear: 325-340mm
Pressure: 282psi


The picture above shows the rear displacer unit with the rod and aluminium fitting to the rubber diaphragm. The end of the rod (opposite to tapered end) can be shortened. In the DPR Motorsport Metro, this rod has been shortened by 15mm and the ride height set to 280 mm between the wheel centre and the wheel arch.
The best approach is to measure the ride height at the hydrolastic pressure that provides the normal ride height , depressurise & shorten the rod by a fixed amount, e.g. 5mm. Then refit, repressurise to the same pressure and measure the ride height to see how much the car has dropped. For road cars, 5mm off this rod may be enough. You can then estimate the amount to remove to get to the desired ride height - but err on the lower amount as it is difficult to put back metal. You will need to bounce the car around to allow the suspension to reach a stable ride height.
The picture above omits the helper springs - provided that the droop stop modification below is made, these springs are not required but if refitted they may need shortening.
Once you have one side at the correct ride height, you should shorten the other side to exactly the same length.