X1500 will run on unleaded fine.... all (post 79) have the same valve seats and valves that are compatible with unleaded fuels.
Electronic ignition is easiest to get from another model of Fiat with a sohc engine. What country do you live in? If you have other later models of Fiat (like Regata or even Lancia Delta) you should be able to source the entire setup from one. I would try use the Bosch unit first (reliability) Marelli Plex is very good too, but seem to have regular failures of ECU, and stator / lead.
They differ from the conventional point type, in that the coil trigger is provided by a four-pole reluctor (this is integral with the distributor shaft) which sweeps past a fixed stator pole. (this is mounted where you would expect the points to be) As the reluctor rotates and passes the stator, a magnetic pulse is created, breaking the coil primary circuit (low tension) via a transistorised electronic module thus generating the (high tension) voltage in the secondary winding.
This system has no electronic control over the timing of the spark but it does deliver the spark consistently and reliably. It works 100 % or not at all. The 2 components that fail, usually heat related, are the stator and lead and the ECM. I have never replaced either of these on the bosch unit, but have many times on the Marelli units
There are also aftermarket units that fit into your existing distributor, like Lumenition, that replaces the points with an optical trigger
SteveC
