Grotere benzinetank / Larger fuel tank 1800E(S)

Did someone find a way to mount a larger fuel tank (60-75+ liter) on an Volvo 1800ES? Like to retain the inside cargo capacity and behind the existing fuel tank is quite some space available - see this very nice picture I found on the Internet.

This car seems to have a high capacity fuel tank as well (28 Gallon?)
www.bonhams.com/auctions/21916/lot/334/

Suggestions (and photos) appreciated!
Suggesties (en fotos) worden zeer gewaardeerd!

Bart Schilt