to start with

the dizzy you got from the US, do you get any engine codes with it. There is no reson you should not be able to set the timing unless your valve timing is incorectly set. ( dont mess with it unless you know what your doing )

the internals of the TD43 should fit and allow the TD44 to run as long as they are both OBDI. You need to ensure you place the CKP, TDC and CYP reluctor in the correct location in respect to what you have on the shaft. Also the air gap between the reluctor pickup and the teeth on the shaft is vital. If then youu have wired the ICM and coil you will be OK.

in what way did yor original dizzy fail ?