It seems the previous owner has fitted the wrong type of coil - a Lucas DLB105 sport coil. This has a primary resistance of 3 Ohms.
The 65DM4 dizzy needs less than 1 Ohm, which the GCL143 provides.
Over time, this has possibly burnt out the ignition module.
Edited by Readers14, 21 June 2017 - 07:57 PM.