[AlfistiSA]

But didn't he install a 1500cc kit?

Is it known what the Alfa technicians actually learned from Doug?

!500cc kit yes, but as I understand it, amongst the tricks that Doug used was to close up the 14mm plug holes, re-drill and fit 10mm plugs. This allowed him to fit larger valve seats to the head for bigger valves. It became a standard trick through the racing fraternity out here. The Cooper Alfa had the same treatment --> 1957 Cooper Alfa T43 chassis number F2.22.57 - Old Cars

I wasn't around at the time, so am repeating what I heard while growing up

Ciao
Greig