Hi-
The US market first production 1978 car was 9288200011, so that would be production (factory number) #1. I used to own 9288200021, which is listed in the registry as #0011. So for 1978 you just subtract 10 from the last 4 of the VIN and that's your production number
The same is true for 1979, so your production number should be #374 for the US market.
The 78-79 5-speed no sunroof and manual seats is a great combination, as is the Petrol and Cork. I helped a friend restore a '78 Minverva Blue/ Cork car, love the combo.
A couple of 928 guys have access to some of the options documentation for 928s from 1980-95. Unfortunately that does not include the 78s and 79s. You can contact Porsche classic and get a PPS that will list the option codes at :
https://www.pca.org/resource/porsche...thenticity-coa