All the wiring in my new house is run in conduit which acts as the earth.

The conduit terminates in metal boxes approx 5"x"2.5" with the 15 amp
faceplate fixed by four screws in the corners.

Is it possible to buy adaptor plates for these old style boxes or do I have
to replace them and ,if so, how should the earth connection be secured.

Also, is it permissible to run earth connections from the terminals in new
boxes to existing conduit runs fixed by an earthing strap?

TIA