Yeah mine is a 1987 pre defender and they had a tiny tank. The fill capacity from bunny hopping to brimmed is 10 gallons (45 litres sadly at our pumps!) so it may be bigger but you can't get the last drops up10 gallons???!!! Really?! That's an incredibly small tank for something that thirsty! That's small even by "family car" standards. I thought they were nearer 12 gallons? I take your point about using loads of fuel whilst laning, but surely you can top up before the lanes?
Many years ago (early '90s) I had a LWB petrol Series III, which had twin tanks under the seats. Can't remember what the capacity was but even at 1990s prices it could hold £100 of petrol!
Yes I have filled before but if you are doing something like the Strata it is not that easy!!