I checked a 4.0 head to a 258 block swap earlyer and it said that the bore was 98.4mm and I put it onto a metric to standard conversion calculator and it sayed 3.87402 inches, and that it added 40 horsepower and 3-5 miles per allon.
I trust your judgement and you are probably wright, this is just what I found.
Sorry for not finding mm/cc per 10 squirts for the webbers in the Aussie Valliant, I looked at the Aussies, Valliants CHrisler, Aussie Valliants, Webber 45s, tripple 2 barrel for inline six...
...Good luck...