The stock CDI unit had been removed by a previous owner on this motor and it was running on just a 12v coil, so a MSD 6A was fitted along with electronic points and high-gauge ignition leads.
Something was still wrong with the timing curve though, and after investigation into the distributor the answer was revealed. Someone had been tampering with the weights and it just didn’t advance properly. The timing advance curve is critical on these motors, so a second-hand Bosch distributor was sourced (not a cheap task) and it was sent away to be correctly rebuilt and weighted for this motor.