Well I found some photo's. Looks as though after moving a few bits you might get an additional tank between the prop shaft and the chassis rail.
Any other ideas?
View attachment 7792583View attachment 7792584View attachment 7792585View attachment 7792586View attachment 7792587
Looks great do you know if this is a PT2 vehicle? With a moulded plastic tank you could get a fair amount of volume out of that cavity.