I recall thinking about this awhile back. However, I was thinking about the larger 300D Diesel fuel tank which was 20 litres (approx 5 USG) larger.

Would the 500E use the same tank and therefore the same capacity difference? Are there mounting differences? I have no idea - sorry I can't help more.

I have no idea of the work involved but I let go of the idea because of competing priorities.

Cheers,
Paul