I finally had a weather window so have removed the pins to measure them.
So, Ebay list the correct pins for an Alfa GT as 75mm long with an 8mm diameter...
Mine has 2 different pins, the upper pin is 75mm long and has a 10mm diameter, the lower one is 65mm with a varying diameter of 8.6mm ti 9.7mm which of course is closest to the specs of a 147 kit.
I might just get the 147 kit, bin the rubber sleeved pins altogether and just fit the plain pins on the bottom too. Then I won't have to worry about the rubber locking up the caliper like every brake caliper ever made of this design (I had the same problem with a set of Land rover brakes too because of the rubber).