Distributor cap Part number/s ??

[124cso]

I am trying to locate a replacement/spare distributor cap for my 79 Spider 2000 FI with pointsless ignition. As these were never brought to my part of the world, it is proving difficult. The 1608cc BC Coupes came here but my cap is about an inch taller to accomodate the module.
Can anyone tell me the part number for the correct cap so I can look at cross-reference charts ?
Either a Marelli, Bremi, Bosch or lucas number anyone ??
My cap has no numbering on it and is of the 'flat top' type.