Nice find there. That motor spares would be best to contact CMB themselves.

Lots info can be found here
http://www.modelboatracing.co.uk/
Good guy to try also is Ian Folksen http://www.iansboats.co.uk/
Or Dave Marles http://www.prestwich.ndirect.co.uk/

Both these two guys should be able to either have or find you spares for the 4 bolt 90. They were strong motors.

The hull looks like a shelack bottom with a delfini dek.

Cobus